common/cmd_mdio.c: fix compile warning

cmd_mdio.c: In function 'mdio_read_ranges':
cmd_mdio.c:97: warning: comparison is always false due to limited range of data type

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Cc: Andy Fleming <afleming@freescale.com>

common/cmd_mdio.c

@@ -91,9 +91,9 @@ int mdio_read_ranges(struct mii_dev *bus, int addrlo,
 
 		for (devad = devadlo; devad <= devadhi; devad++) {
 			for (reg = reglo; reg <= reghi; reg++) {
-				u16 val;
-				val = bus->read(bus, addr, devad, reg);
+				int val;
 
+				val = bus->read(bus, addr, devad, reg);
 				if (val < 0) {
 					printf("Error\n");