usb: gadget: uvc: fix missing mutex_unlock() if kstrtou8() fails

commit 7ebb605 upstream.

If kstrtou8() fails, the mutex_unlock() is missed, move kstrtou8()
before mutex_lock() to fix it up.

Fixes: 0525210 ("usb: gadget: uvc: Allow definition of XUs in configfs")
Fixes: b3c839b ("usb: gadget: uvc: Make bSourceID read/write")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20230213070926.776447-1-yangyingliang@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/uvc_configfs.c

@@ -524,17 +524,17 @@ static ssize_t uvcg_default_output_b_source_id_store(struct config_item *item,
 	int result;
 	u8 num;
 
+	result = kstrtou8(page, 0, &num);
+	if (result)
+		return result;
+
 	mutex_lock(su_mutex); /* for navigating configfs hierarchy */
 
 	opts_item = group->cg_item.ci_parent->ci_parent->
 			ci_parent->ci_parent;
 	opts = to_f_uvc_opts(opts_item);
 	cd = &opts->uvc_output_terminal;
 
-	result = kstrtou8(page, 0, &num);
-	if (result)
-		return result;
-
 	mutex_lock(&opts->lock);
 	cd->bSourceID = num;
 	mutex_unlock(&opts->lock);