[SPARC64]: Fix booting on V100 systems.

On the root PCI bus, the OBP device tree lists device 3 twice.
Once as 'pm' and once as 'lomp'.

Everything goes downhill from there.

Ignore the second instance to workaround this.

Thanks to Kövedi_Krisztián for the bug report and
testing the fix.

Signed-off-by: David S. Miller <davem@davemloft.net>