ALSA: usb-audio: Use pcm_for_each_format() macro for PCM format iterations

The new macro can fix the sparse warnings gracefully:
  sound/usb/proc.c:73:31: warning: restricted snd_pcm_format_t degrades to integer
  sound/usb/proc.c:73:38: warning: restricted snd_pcm_format_t degrades to integer
  sound/usb/proc.c:73:61: warning: restricted snd_pcm_format_t degrades to integer

No functional changes, just sparse warning fixes.

Link: https://lore.kernel.org/r/20200206163945.6797-4-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>

sound/usb/proc.c

@@ -70,7 +70,7 @@ static void proc_dump_substream_formats(struct snd_usb_substream *subs, struct s
 		snd_iprintf(buffer, "  Interface %d\n", fp->iface);
 		snd_iprintf(buffer, "    Altset %d\n", fp->altsetting);
 		snd_iprintf(buffer, "    Format:");
-		for (fmt = 0; fmt <= SNDRV_PCM_FORMAT_LAST; ++fmt)
+		pcm_for_each_format(fmt)
 			if (fp->formats & pcm_format_to_bits(fmt))
 				snd_iprintf(buffer, " %s",
 					    snd_pcm_format_name(fmt));