[media] media: correct return value in dvb_demux_poll

Data type of return value is unsigned int, but in function of dvb_demux_poll,
when the pointer of dmxdevfilter equals NULL, it will return -EINVAL, which
is invalid.
Signed-off-by: NChangbing Xiong <cb.xiong@samsung.com>
Signed-off-by: NMauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/dvb-core/dmxdev.c

@@ -1088,7 +1088,7 @@ static unsigned int dvb_demux_poll(struct file *file, poll_table *wait)
 	unsigned int mask = 0;
 
 	if (!dmxdevfilter)
-		return -EINVAL;
+		return POLLERR;
 
 	poll_wait(file, &dmxdevfilter->buffer.queue, wait);