[media] mx3-camera: locking cleanup in mx3_videobuf_queue()

Smatch complains about the locking here because we mix spin_lock_irq()
with spin_lock_irqsave() in an unusual way.  According to Smatch, it's
not always clear if the IRQs are enabled or disabled when we return.  It
turns out this function is always called with IRQs enabled and we can
just use spin_lock_irq().
It's called from __enqueue_in_driver().

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>