media: ccs-pll: Use correct VT divisor for calculating VT SYS divisor

Use the correct video timing divisor to calculate the SYS divisor. Instead
of the current value, the minimum was used. This could have resulted in a
too low SYS divisor.

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