macintosh: windfarm: Another convert to using %pOFn instead of device_node.name

In preparation to remove the node name pointer from struct
device_node, convert printf users to use the %pOFn format specifier.

Convert the open coded iterating thru child nodes to
for_each_child_of_node() while we're here.

Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>