media: v4l2-mem2mem: Rename v4l2_m2m_buf_copy_data to v4l2_m2m_buf_copy_metadata

The v4l2_m2m_buf_copy_data helper is used to copy the buffer
metadata, such as its timestamp and its flags.

Therefore, the v4l2_m2m_buf_copy_metadata name is more clear
and avoids confusion with a payload data copy.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
[hverkuil-cisco@xs4all.nl: also fix cedrus_dec.c]
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>