media: vb2: check memory model for VIDIOC_CREATE_BUFS

vb2_core_create_bufs did not check if the memory model for newly added
buffers is the same as for already existing buffers. It should return an
error if they aren't the same.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reported-by:  <syzbot+e1fb118a2ebb88031d21@syzkaller.appspotmail.com>
Cc: <stable@vger.kernel.org>      # for v4.16 and up
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>