of/sparc: fix build regression from of_device changes

Commit id 1636f8ac (sparc/of: Move
of_device fields into struct pdev_archdata) missed fixing up the
n2_core.c and greth.c drivers.  This patch makes the required changes.

Reported-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>