net/ibm/emac: fix type of phy_mode

phy_mode can be negative.

The problem has been detected using proposed semantic patch
scripts/coccinelle/tests/unsigned_lesser_than_zero.cocci [1].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2038576

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/ibm/emac/core.h

@@ -181,7 +181,7 @@ struct emac_instance {
 	struct mal_commac		commac;
 
 	/* PHY infos */
-	u32				phy_mode;
+	int				phy_mode;
 	u32				phy_map;
 	u32				phy_address;
 	u32				phy_feat_exc;