firmware-utils: mkplanexfw: fix compiler warnings/errors
mkplanexfw.c:108:21: error: unused variable ‘board’ [-Werror=unused-variable]
mkplanexfw.c:233:24: error: pointer targets in passing argument 2 of ‘sha1_update’ differ in signedness [-Werror=pointer-sign]
mkplanexfw.c:251:2: error: label ‘out_flush’ defined but not used [-Werror=unused-label]
mkplanexfw.c:224:2: error: ignoring return value of ‘fread’, declared with attribute warn_unused_result [-Werror=unused-result]
Signed-off-by: Petr Štetiar <ynezz@true.cz>