media: v4l-common: Make v4l2_find_nearest_size more sparse-friendly

This sparse warning is emitted by using v4l2_find_nearest_size in some
cases. Fix it in the framework.

>> drivers/media/i2c/ov5640.c:1394:14: sparse: incorrect type in assignment
+(different base types) @@    expected struct ov5640_mode_info const *mode @@
+got ststruct ov5640_mode_info const *mode @@
   drivers/media/i2c/ov5640.c:1394:14:    expected struct ov5640_mode_info const
+*mode
   drivers/media/i2c/ov5640.c:1394:14:    got struct ov5640_mode_info const ( *<
+noident> )[9]

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