[media] v4l: omap4iss: Restore irq flags correctly in omap4iss_video_buffer_next()

The spin_lock_irqsave() macro is not nestable.  The second call will
overwrite the first record of "flags" so the IRQs will not be enabled
correctly at the end of the function.

In the current code, this function is always called from the IRQ handler
so everything works fine and this fix doesn't change anything.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>