Add macro to compare two v4l2_fract values in v4l2 common internal API.
The same macro FRACT_CMP() is used by vivid and bcm2835-camera.  This just
renames it to V4L2_FRACT_COMPARE in order to avoid namespace collision.

Cc: Matt Ranostay <matt.ranostay@konsulko.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>