powerpc/vio: Use put_device() on device_register failure

The kernel doc for device_register (and device_initialize) very clearly
state to call put_device not kfree after calling, even on error.

Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>