ALSA: usb-audio: Fix uninitialized variable at __uac_clock_find_source()

The cur variable indicating the currently selected clock source can be
theoretically used as uninitialized after the recent commit
481f17c4 ("ALSA: usb-audio: Handle error for the current selector
gracefully").  For addressing it, initialize it before use.

Also, one place seems setting 0 to a wrong variable ret, instead of
cur; otherwise it makes little sense.  Since the initialization is
done beforehand, we can get rid of this line, too.

Fixes: 481f17c4 ("ALSA: usb-audio: Handle error for the current selector gracefully")
Reported-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/4b261d68-f53f-240d-2d8a-2f88b337849d@canonical.com
Link: https://lore.kernel.org/r/s5hfsyhh97t.wl-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/clock.c

@@ -290,6 +290,7 @@ static int __uac_clock_find_source(struct snd_usb_audio *chip,
 		pins = GET_VAL(selector, proto, bNrInPins);
 		clock_id = GET_VAL(selector, proto, bClockID);
 		sources = GET_VAL(selector, proto, baCSourceID);
+		cur = 0;
 
 		if (pins == 1) {
 			ret = 1;
@@ -314,7 +315,6 @@ static int __uac_clock_find_source(struct snd_usb_audio *chip,
 
 			if (!chip->autoclock)
 				return -EINVAL;
-			ret = 0;
 			goto find_others;
 		}