media: st-mipid02: add a check for devm_gpiod_get_optional

mipid02_probe misses a check for devm_gpiod_get_optional and may miss
the failure.
Add a check to fix the problem.

Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>