ALSA: sound/usb/usx2y: fix sparse warning: Should it be static?

Impact: Move declaration to header file.

Fix this sparse warning:
  sound/usb/usx2y/usx2yhwdeppcm.c:739:5: warning: symbol 'usX2Y_hwdep_pcm_new' was not declared. Should it be static?

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/usb/usx2y/usx2yhwdeppcm.h b/sound/usb/usx2y/usx2yhwdeppcm.h
index c3382fd..9c4fb84 100644
--- a/sound/usb/usx2y/usx2yhwdeppcm.h
+++ b/sound/usb/usx2y/usx2yhwdeppcm.h
@@ -18,3 +18,5 @@
 	volatile unsigned captured_iso_frames;
 	int capture_iso_start;
 };
+
+int usX2Y_hwdep_pcm_new(struct snd_card *card);