media: rockchip/rga: constify v4l2_m2m_ops structure

The v4l2_m2m_ops structure can be const as it is only passed to
v4l2_m2m_init whose parameter is const.

Done with the help of Coccinelle.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>