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>