Calculate pixel-rate at run time instead of compile time.

Instead of using hardcoded pixels-per-line, extract it from current sensor
mode.
Signed-off-by: NChiranjeevi Rapolu <chiranjeevi.rapolu@intel.com>
Signed-off-by: NSakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@osg.samsung.com>