media: ccs-pll: Better validate VT PLL branch

[ Upstream commit cd9cb031 ]

Check that the VT PLL dividers are actually found, don't trust they always
are even though they should be.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Sasha Levin <sashal@kernel.org>