net/core: Do not clear VF index for node/port GUIDs query

VF numbers were assigned to node_guid and port_guid, but cleared
right before such query calls were issued. It caused to return
node/port GUIDs of VF index 0 for all VFs.

Fixes: 30aad417

 ("net/core: Add support for getting VF GUIDs")
Reported-by: Adrian Chiris <adrianc@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>