powerpc/83xx: Update ranges in gianfar node to match other dts

The gianfar@25000 node was missing its ranges prop for the mdio bus
and provided an explicit ranges property on gianfar@24000 to match
change from commit:

commit 70b3adbba056f5d9081f1ec9b4a629e3c7502072
Author: Anton Vorontsov <avorontsov@ru.mvista.com>
Date:   Thu Mar 19 21:01:45 2009 +0300

    powerpc/83xx: Move gianfar mdio nodes under the ethernet nodes

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>