ALSA: usb-audio - Fix invalid volume resolution on Logitech HD webcam c270

USB audio driver spews an error message when probing Logitech HD
webcam c270:
  ALSA mixer.c:1300 usb_audio: Warning! Unlikely big volume range (=6144), cval->res is probably wrong.
  ALSA mixer.c:1304 usb_audio: [5] FU [Mic Capture Volume] ch = 1, val = 1536/7680/1

Obviously the device needs a fixed volume resolution (cval->res = 384)
like other Logitech devices.

Bugzilla: https://bugzilla.novell.com/show_bug.cgi?id=821735Reported-and-tested-by: Cristian Rodríguez <crrodriguez@opensuse.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer.c

@@ -886,6 +886,7 @@ static void volume_control_quirks(struct usb_mixer_elem_info *cval,
 	case USB_ID(0x046d, 0x0808):
 	case USB_ID(0x046d, 0x0809):
 	case USB_ID(0x046d, 0x081d): /* HD Webcam c510 */
+	case USB_ID(0x046d, 0x0825): /* HD Webcam c270 */
 	case USB_ID(0x046d, 0x0991):
 	/* Most audio usb devices lie about volume resolution.
 	 * Most Logitech webcams have res = 384.