media: ipu3-cio2: Fix pixel-rate derived link frequency

The driver uses v4l2_get_link_freq() helper to obtain the link frequency
using the LINK_FREQ but also the PIXEL_RATE control. The divisor for the
pixel rate derived link frequency was wrong, missing the bus uses double
data rate. Fix this.

Reported-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Fixes: 4b6c129e ("media: ipu3-cio2: Use v4l2_get_link_freq helper")
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Bingbu Cao <bingbu.cao@intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>