[media] v4l: mt9t001: constify v4l2_subdev_internal_ops structure

This v4l2_subdev_internal_ops structure is never modified.  All other
v4l2_subdev_internal_ops structures are declared as const.

Done with the help of Coccinelle.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>