[SCSI] qla2xxx: Add checks for a valid fcport in dev-loss-tmo/terminate_rport_io callbacks.

Commit f78badb1 ([SCSI] fc
transport: pre-emptively terminate i/o upon dev_loss_tmo timeout)
changed the callback semantics of dev_loss_tmo and
terminate_rport_io such that repeated calls could be made.  This
could result in the the driver using stale (NULLed-out, in
dev_loss_tmo) data from the rport.  Correct this by addint a
simple check to ensure a valid fcport is attached.

Signed-off-by: Seokmann Ju <seokmann.ju@qlogic.com>
Signed-off-by: Andrew Vasquez <andrew.vasquez@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>