[ALSA] Fix pcm-draining of capture stream in PCM middle layer

Fix the draining of PCM capture stream in the PCM middle layer.
snd_pcm_drain() ignored capture streams, but it should change
the state to SNDRV_PCM_DRAINING.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_native.c

@@ -1469,8 +1469,6 @@ static int snd_pcm_drain(struct snd_pcm_substream *substream)
 		}
 	}
 	up_read(&snd_pcm_link_rwsem);
-	if (! num_drecs)
-		goto _error;
 
 	snd_pcm_stream_lock_irq(substream);
 	/* resume pause */