media: hantro: Move copy_metadata() before doing a decode operation

Some decoders use intra slice/frame references. The capture buffer
pointed by these references might be new and thus have invalid
timestamp which prevents the decoder logic from retrieving the
vb2_buffer object based on the output buf timestamp.
Copy all metadata (including the timestamp) before starting the decode
operation.

Suggested-by: Jonas Karlman <jonas@kwiboo.se>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Tested-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>