Revert "ALSA: usb-audio: Disable Lenovo P620 Rear line-in volume control"

This reverts commit 34dedd2.

According to Realtek, volume FU works for line-in.

I can confirm volume control works after device firmware is updated.

Fixes: 34dedd2 ("ALSA: usb-audio: Disable Lenovo P620 Rear line-in volume control")
Signed-off-by: Kai-Heng Feng <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Takashi Iwai <[email protected]>

Author: khfeng

sound/usb/mixer_maps.c

@@ -371,7 +371,6 @@ static const struct usbmix_name_map asus_rog_map[] = {
 };
 
 static const struct usbmix_name_map lenovo_p620_rear_map[] = {
-	{ 19, NULL, 2 }, /* FU, Volume */
 	{ 19, NULL, 12 }, /* FU, Input Gain Pad */
 	{}
 };