kernel: ltq-vdsl-vr9: fix multiple compilation warning

kernel: ltq-vdsl-vr9: fix multiple compilation warning

Fix multiple compilation warning for fallthrough and unused functions.
Fix compilation warning:
home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xrx200/drv_dsl_cpe_api-4.17.18.6/src/device/drv_dsl_cpe_device_vrx.c: In function 'DSL_DRV_VRX_TestParametersFeUpdate':
/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xrx200/drv_dsl_cpe_api-4.17.18.6/src/device/drv_dsl_cpe_device_vrx.c:3359:17: error: unused variable 'nMsgId' [-Werror=unused-variable]
 3359 |    DSL_uint16_t nMsgId = EVT_PMD_TESTPARAMSGET;
      |                 ^~~~~~
/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xrx200/drv_dsl_cpe_api-4.17.18.6/src/device/drv_dsl_cpe_device_vrx.c: In function 'DSL_DRV_DEV_AutobootHandleTraining':
/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xrx200/drv_dsl_cpe_api-4.17.18.6/src/device/drv_dsl_cpe_device_vrx.c:8310:19: error: this statement may fall through [-Werror=implicit-fallthrough=]
 8310 |          bPreFail = DSL_TRUE;
      |          ~~~~~~~~~^~~~~~~~~~
/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xrx200/drv_dsl_cpe_api-4.17.18.6/src/device/drv_dsl_cpe_device_vrx.c:8316:7: note: here
 8316 |       case DSL_LINESTATE_EXCEPTION:
      |       ^~~~
cc1: all warnings being treated as errors

/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xrx200/drv_dsl_cpe_api-4.17.18.6/src/pm/drv_dsl_cpe_pm_core.c: In function 'DSL_DRV_PM_CountersReset':
/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xrx200/drv_dsl_cpe_api-4.17.18.6/src/pm/drv_dsl_cpe_pm_core.c:2328:7: error: this statement may fall through [-Werror=implicit-fallthrough=]
 2328 |    if (ResetType == DSL_PM_RESET_HISTORY)
      |       ^
/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xrx200/drv_dsl_cpe_api-4.17.18.6/src/pm/drv_dsl_cpe_pm_core.c:2331:4: note: here
 2331 |    case DSL_PM_RESET_TOTAL:
      |    ^~~~
cc1: all warnings being treated as errors

/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xrx200/drv_dsl_cpe_api-4.17.18.6/src/common/drv_dsl_cpe_os_linux.c: In function 'DSL_ModuleCleanup':
/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xrx200/drv_dsl_cpe_api-4.17.18.6/src/common/drv_dsl_cpe_os_linux.c:1266:13: error: assignment to 'dev_t' {aka 'unsigned int'} from 'void *' makes integer from pointer without a cast [-Werror=int-conversion]
 1266 |    dsl_devt = NULL;
      |             ^
/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xrx200/drv_dsl_cpe_api-4.17.18.6/src/common/drv_dsl_cpe_os_linux.c: At top level:
/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xrx200/drv_dsl_cpe_api-4.17.18.6/src/common/drv_dsl_cpe_os_linux.c:1178:13: error: 'DSL_DRV_NlSendMsg' defined but not used [-Werror=unused-function]
 1178 | static void DSL_DRV_NlSendMsg(DSL_char_t* pMsg)
      |             ^~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_xrx200/drv_dsl_cpe_api-4.17.18.6/src/device/drv_dsl_cpe_msg_vrx.c:2459:20: error: 'DSL_DRV_VRX_SpreadArray' defined but not used [-Werror=unused-function]
 2459 | static DSL_Error_t DSL_DRV_VRX_SpreadArray(
      |                    ^~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>