mfd: sm501: Add check for platform_driver_register()

As platform_driver_register() can return error numbers,
it should be better to check platform_driver_register()
and deal with the exception.

Fixes: b6d6454f ("[PATCH] mfd: SM501 core driver")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20220913091112.1739138-1-jiasheng@iscas.ac.cn