media: ccs-pll: Fix link frequency for C-PHY

The highest fundamental frequency signal for C-PHY is half of the symbol
rate which is similar to D-PHY. Take this into account in ccs-pll.

Also remove the outdated comment.

Fixes: 8030aa4f ("media: ccs-pll: Add C-PHY support")
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>