[SCSI] zfcp: Fix opening of wka ports

Running two wka_port_get calls in parallel could issue two open_port
requests, overwriting the port handle. Don't issue an open_port
for the state PORT_OPENING, and only read the data from GOOD
responses.

Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Acked-by: Swen Schillig <swen@vnet.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>