ALSA: fix pcm.h kernel-doc warning and notation

Fix kernel-doc warning in <sound/pcm.h> and add function name to make
the kernel-doc notation complete.

Warning(include/sound/pcm.h:1081): No description found for parameter 'substream'
Signed-off-by: NRandy Dunlap <rdunlap@xenotime.net>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

include/sound/pcm.h

@@ -1075,7 +1075,8 @@ static inline void snd_pcm_limit_isa_dma_size(int dma, size_t *max)
 const char *snd_pcm_format_name(snd_pcm_format_t format);
 
 /**
- * Get a string naming the direction of a stream
+ * snd_pcm_stream_str - Get a string naming the direction of a stream
+ * @substream: the pcm substream instance
  */
 static inline const char *snd_pcm_stream_str(struct snd_pcm_substream *substream)
 {