media: exynos4-is: Add missed check for pinctrl_lookup_state()

fimc_md_get_pinctrl() misses a check for pinctrl_lookup_state().
Add the missed check to fix it.

Fixes: 4163851f ("[media] s5p-fimc: Use pinctrl API for camera ports configuration]")
Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>