media: rockchip/vpu: Use v4l2_m2m_buf_copy_metadata

Use the recently introduced v4l2_m2m_buf_copy_metadata helper
and get rid of some code.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>