ALSA: scarlett2: Add missing error check to scarlett2_usb_set_config()

scarlett2_usb_set_config() calls scarlett2_usb_get() but was not
checking the result. Return the error if it fails rather than
continuing with an invalid value.
Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Fixes: 9e15fae6 ("ALSA: usb-audio: scarlett2: Allow bit-level access to config")
Link: https://lore.kernel.org/r/def110c5c31dbdf0a7414d258838a0a31c0fab67.1703001053.git.g@b4.vuSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer_scarlett2.c

@@ -1577,7 +1577,10 @@ static int scarlett2_usb_set_config(
 		size = 1;
 		offset = config_item->offset;
 
-		scarlett2_usb_get(mixer, offset, &tmp, 1);
+		err = scarlett2_usb_get(mixer, offset, &tmp, 1);
+		if (err < 0)
+			return err;
+
 		if (value)
 			tmp |= (1 << index);
 		else