ALSA: Re-export snd_pcm_format_name() function

Re-export snd_pcm_format_name() function to be used outside the PCM core.
As a first example, usbaudio is changed to use it now again.

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

include/sound/pcm.h

@@ -965,4 +965,6 @@ static inline void snd_pcm_limit_isa_dma_size(int dma, size_t *max)
 
 #define PCM_RUNTIME_CHECK(sub) snd_BUG_ON(!(sub) || !(sub)->runtime)
 
+const char *snd_pcm_format_name(snd_pcm_format_t format);
+
 #endif /* __SOUND_PCM_H */