[media] vsp1: set V4L2_CTRL_FLAG_MODIFY_LAYOUT for histogram controls

The two histogram controls will modify the layout of the
metadata, so this flag should be set.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>