ALSA: usb-audio: fix uninitialized variable compile warning

Fix the following warning when optimizing for size with gcc-4.6.4:
sound/usb/mixer_quirks.c:1514:6: warning: 'err' may be used uninitialized in this function [-Wuninitialized]
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer_quirks.c

@@ -1603,7 +1603,7 @@ static int snd_microii_controls_create(struct usb_mixer_interface *mixer)
 			return err;
 	}
 
-	return err;
+	return 0;
 }
 
 int snd_usb_mixer_apply_create_quirk(struct usb_mixer_interface *mixer)