media: rkisp1: Fix line stride calculation

The line stride is expressed in the hardware as a number of pixels for
the first plane. The bytesperline must thus be a multiple of the first
plane's bpp value. Enforce this constraint.

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