ALSA: pcm: Fix poll error return codes

We can't return a negative error code from the poll callback the return
type is unsigned and is checked against the poll specific flags we need
to return POLLERR if we encounter an error.
Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_native.c

@@ -3161,7 +3161,7 @@ static unsigned int snd_pcm_playback_poll(struct file *file, poll_table * wait)
 
 	substream = pcm_file->substream;
 	if (PCM_RUNTIME_CHECK(substream))
-		return -ENXIO;
+		return POLLOUT | POLLWRNORM | POLLERR;
 	runtime = substream->runtime;
 
 	poll_wait(file, &runtime->sleep, wait);
@@ -3200,7 +3200,7 @@ static unsigned int snd_pcm_capture_poll(struct file *file, poll_table * wait)
 
 	substream = pcm_file->substream;
 	if (PCM_RUNTIME_CHECK(substream))
-		return -ENXIO;
+		return POLLIN | POLLRDNORM | POLLERR;
 	runtime = substream->runtime;
 
 	poll_wait(file, &runtime->sleep, wait);