i2c: diolan-u2c: Fix master_xfer return code

The master_xfer function returns 0 on success. It should return the number of
successful transactions.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>

drivers/i2c/busses/i2c-diolan-u2c.c

@@ -405,6 +405,7 @@ static int diolan_usb_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs,
 			}
 		}
 	}
+	ret = num;
 abort:
 	sret = diolan_i2c_stop(dev);
 	if (sret < 0 && ret >= 0)