ALSA: usb-audio: scarlett_gen2: Fix -Wformat-truncation warning

The recent enablement of -Wformat-truncation leads to a false-positive
warning for mixer_scarlett_gen2.c.

For suppressing the warning, replace snprintf() with scnprintf().
As stated in the above, truncation doesn't matter.

Link: https://lore.kernel.org/r/20230915082802.28684-4-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer_scarlett_gen2.c

@@ -3218,8 +3218,8 @@ static int scarlett2_add_line_in_ctls(struct usb_mixer_interface *mixer)
 			int from = i * info->inputs_per_phantom + 1;
 			int to = (i + 1) * info->inputs_per_phantom;
 
-			snprintf(s, sizeof(s), fmt2, from, to,
-				 "Phantom Power", "Switch");
+			scnprintf(s, sizeof(s), fmt2, from, to,
+				  "Phantom Power", "Switch");
 			err = scarlett2_add_new_ctl(
 				mixer, &scarlett2_phantom_ctl,
 				i, 1, s, &private->phantom_ctls[i]);