[ALSA] usbaudio - Coping with short replies in usbmixer

This patch makes sure that short USB replies are treated as an
error when requesting the value of a certain mixer control.

Signed-off-by: Thomas Reitmayr <[e-mail]>
Signed-off-by: Takashi Iwai <[e-mail]>
Signed-off-by: Jaroslav Kysela <[e-mail]>

sound/usb/usbmixer.c

···
 				    request,
 				    USB_RECIP_INTERFACE | USB_TYPE_CLASS | USB_DIR_IN,
 				    validx, cval->mixer->ctrlif | (cval->id << 8),
-				    buf, val_len, 100) >= 0) {
+				    buf, val_len, 100) >= val_len) {
 			*value_ret = convert_signed_value(cval, snd_usb_combine_bytes(buf, val_len));
 			return 0;
 		}