usb: gadget: f_ncm: fix missing unlock on error in ncm_alloc()

Add the missing unlock before return from function ncm_alloc()
in the error handling case.

Introduced by commit e7306603.
(usb: gadget: f_ncm: add configfs support)
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/f_ncm.c

@@ -1403,6 +1403,7 @@ struct usb_function *ncm_alloc(struct usb_function_instance *fi)
 				      sizeof(ncm->ethaddr));
 	if (status < 12) { /* strlen("01234567890a") */
 		kfree(ncm);
+		mutex_unlock(&opts->lock);
 		return ERR_PTR(-EINVAL);
 	}
 	ncm_string_defs[STRING_MAC_IDX].s = ncm->ethaddr;