ALSA: usb-audio: scarlett2: snd_scarlett_gen2_controls_create() can be static

sound/usb/mixer_scarlett_gen2.c:2000:5: warning: symbol 'snd_scarlett_gen2_controls_create' was not declared. Should it be static?

Fixes: 265d1a90 ("ALSA: usb-audio: scarlett2: Improve driver startup messages")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/r/20210522180900.GA83915@f59a3af2f1d9Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer_scarlett_gen2.c

@@ -1997,7 +1997,7 @@ static int scarlett2_mixer_status_create(struct usb_mixer_interface *mixer)
 	return usb_submit_urb(mixer->urb, GFP_KERNEL);
 }
 
-int snd_scarlett_gen2_controls_create(struct usb_mixer_interface *mixer,
+static int snd_scarlett_gen2_controls_create(struct usb_mixer_interface *mixer,
 					     const struct scarlett2_device_info *info)
 {
 	int err;