V4L/DVB (12424): soc-camera: fix recursive locking in .buf_queue()

The .buf_queue() V4L2 driver method is called under
spinlock_irqsave(q->irqlock,...), don't take the lock again inside the
function.

Reported-by: Antonio Ospite <ospite@studenti.unina.it>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>