[media] media: davinci: vpfe: fix build error

recent patch with commit id 4f996594
which makes vidioc_s_crop const, was causing a following build error.
vpfe_capture.c: In function 'vpfe_s_crop':
vpfe_capture.c:1695: error: assignment of read-only location '*crop'
vpfe_capture.c:1706: warning: passing argument 1 of
'ccdc_dev->hw_ops.set_image_window' discards qualifiers from pointer target type
vpfe_capture.c:1706: note: expected 'struct v4l2_rect *' but argument is of
type 'const struct v4l2_rect *'
make[4]: *** [drivers/media/platform/davinci/vpfe_capture.o] Error 1

Signed-off-by: Lad, Prabhakar <prabhakar.lad@ti.com>
Signed-off-by: Manjunath Hadli <manjunath.hadli@ti.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>