[media] mx2_camera: use GFP_ATOMIC under spin lock

Found using the following semantic patch:
<spml>
@@
@@
spin_lock_irqsave(...);
... when != spin_unlock_irqrestore(...);
* GFP_KERNEL
</spml>

Signed-off-by: Cyril Roelandt <tipecaml@gmail.com>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>