[media] s5p-fimc: fix compiler warning

drivers/media/platform/s5p-fimc/fimc-m2m.c:561:2: warning: passing argument 2 of 'fimc_m2m_try_crop' discards 'const' qualifier from pointer target type [enabled by default]
drivers/media/platform/s5p-fimc/fimc-m2m.c:502:12: note: expected 'struct v4l2_crop *' but argument is of type 'const struct v4l2_crop *'
This is fall-out from this commit:
commit 4f996594


Author: Hans Verkuil <hans.verkuil@cisco.com>
    [media] v4l2: make vidioc_s_crop const

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>