[media] media: i.MX27 camera: Use spin_lock() inside the IRQ handler

We don't need to use spin_lock_irqsave() since there are not
any other IRQs that can race with this ISR.

Signed-off-by: Javier Martin <javier.martin@vista-silicon.com>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>