ALSA: usb-audio: correct the value cache check.

commit 6aa6925c upstream.

The check of cval->cached should be zero-based (including master channel).
Signed-off-by: Yao-Wen Mao <yaowen@google.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

sound/usb/mixer.c

@@ -2529,7 +2529,7 @@ static int restore_mixer_value(struct usb_mixer_elem_info *cval)
 		for (c = 0; c < MAX_CHANNELS; c++) {
 			if (!(cval->cmask & (1 << c)))
 				continue;
-			if (cval->cached & (1 << c)) {
+			if (cval->cached & (1 << (c + 1))) {
 				err = set_cur_mix_value(cval, c + 1, idx,
 							cval->cache_val[idx]);
 				if (err < 0)