[media] usbtv: fix v4l2-compliance issues

Running v4l2-compliance on my usbtv stick revealed two failures:

1) Correct handling of CREATE_BUFS in usbtv_queue_setup was missing. Added this.
2) The sequence counter wasn't reset to 0 when starting streaming.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>