powerpc/85xx: fix typo in p1010rdb.dtsi

Fix typo introduced by "powerpc: Add TBI PHY node to first MDIO bus"
from Andy Fleming.
It's device_type rather than device-type, which causes the mdio probe to
fail thus making all gianfar ethernet interfaces unusable.
Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/boot/dts/p1010rdb.dtsi

@@ -196,7 +196,7 @@ phy2: ethernet-phy@2 {
 		};
 
 		tbi-phy@3 {
-			device-type = "tbi-phy";
+			device_type = "tbi-phy";
 			reg = <0x3>;
 		};
 	};