sunhme: Don't match PCI devices in SBUS probe.

Unfortunately, the OF device tree nodes for SBUS and PCI
hme devices have the same device node name on some systems.

So if the name of the parent node isn't 'sbus', skip it.

Based upon an excellent report and detective work by
Meelis Roos and Eric Brower.

Signed-off-by: David S. Miller <davem@davemloft.net>
Tested-by: Meelis Roos <mroos@linux.ee>