ramips: 6.1: pinctrl: fix compilation with 6.1

ramips: 6.1: pinctrl: fix compilation with 6.1

Upstream changed in ed5c2f5fd10d ("i2c: Make remove callback return void")
the i2c driver's remove function to return no value. Adapt the driver code
to compile with 5.15 and 6.1 like it is done in other projects [0].

Fixes errors in the form of:
  make[8]: Leaving directory '/home/nick/openwrt/build_dir/target-mipsel_24kc_musl/linux-ramips_mt7621/linux-6.1.29'
    CC      drivers/pinctrl/pinctrl-aw9523.o
  drivers/pinctrl/pinctrl-aw9523.c:1117:19: error: initialization of 'void (*)(struct i2c_client *)' from incompatible pointer type 'int (*)(struct i2c_client *)' [-Werror=incompatible-pointer-types]
 1117 |         .remove = aw9523_remove,
      |                   ^~~~~~~~~~~~~
  drivers/pinctrl/pinctrl-aw9523.c:1117:19: note: (near initialization for 'aw9523_driver.remove')
  cc1: all warnings being treated as errors

[0] - https://gitlab.com/ddcci-driver-linux/ddcci-driver-linux/-/merge_requests/10/diffs

Signed-off-by: Nick Hainke <vincent@systemli.org>