[media] omap3isp: Fix histogram regions

This patch fixes a bug which causes all histogram regions to start in the
top left corner of the image. The histogram region coordinates are 16 bit
values which share a 32 bit register. The bug is due to the region end
value assignments overwriting the region start values with zero.

Signed-off-by: Johannes Schellen <Johannes.Schellen@rwth-aachen.de>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>