[media] s5p-g2d: fix compiler warning

drivers/media/platform/s5p-g2d/g2d.c:535:2: warning: passing argument 3 of 'vidioc_try_crop' discards 'const' qualifier from pointer target type [enabled by default]
drivers/media/platform/s5p-g2d/g2d.c:510:12: note: expected 'struct v4l2_crop *' but argument is of type 'const struct v4l2_crop *'
This is fall-out from this commit:
commit 4f996594ceaf6c3f9bc42b40c40b0f7f87b79c86
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>

drivers/media/platform/s5p-g2d/g2d.c

@@ -507,7 +507,7 @@ static int vidioc_g_crop(struct file *file, void *prv, struct v4l2_crop *cr)
 	return 0;
 }
 
-static int vidioc_try_crop(struct file *file, void *prv, struct v4l2_crop *cr)
+static int vidioc_try_crop(struct file *file, void *prv, const struct v4l2_crop *cr)
 {
 	struct g2d_ctx *ctx = prv;
 	struct g2d_dev *dev = ctx->dev;