OF fixups cm_cogent_fixup() and hb_fixup() are supposed to modify the
Linux device tree.  And they did originally, but commit
e520a8c changed them to use
for_each_compatible_node(), which iterates through the Barebox DT.
Use new for_each_compatible_node_from() to specify the Linux DT root
as the start point.

Signed-off-by: Trent Piepho <tpiepho@kymetacorp.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>