[media] s2255drv: fix spinlock issue

qlock spinlock controls access to buf_list and sequence.
qlock spinlock should not be locked during a copy to video buffers, an
operation that may sleep.

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