V4L/DVB (6690): saa7134: fix ignored interrupts

The saa7134 video driver starts dropping frames when used together with the
saa7134-alsa driver. Frames are dropped because when an audio event is waiting
the driver simply ignores the interrupt and passes it on to the saa7134-alsa
interrupt handler. The alsa interrupt handler in turn acknowledges all types
of events thus clearing the pending video events as well. Fix by only masking
out the audio event in the video interrupt handler and by only acknowledging
the audio event in the alsa driver.

Signed-off-by: Heikki Lindholm <holindho@cs.helsinki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>