USB: gadget: u_ether: Fix a configfs return code

If the string is invalid, this should return -EINVAL instead of 0.

Fixes: 73517cf4 ("usb: gadget: add RNDIS configfs options for class/subclass/protocol")
Cc: stable <stable@vger.kernel.org>
Acked-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/YCqZ3P53yyIg5cn7@mwandaSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/u_ether_configfs.h

@@ -182,12 +182,11 @@ out:									\
 						size_t len)		\
 	{								\
 		struct f_##_f_##_opts *opts = to_f_##_f_##_opts(item);	\
-		int ret;						\
+		int ret = -EINVAL;					\
 		u8 val;							\
 									\
 		mutex_lock(&opts->lock);				\
-		ret = sscanf(page, "%02hhx", &val);			\
-		if (ret > 0) {						\
+		if (sscanf(page, "%02hhx", &val) > 0) {			\
 			opts->_n_ = val;				\
 			ret = len;					\
 		}							\