[SCSI] bfa: Fix possible NULL pointer dereference in lunmask add/delete.

Patch fixes the possible NULL pointer dereference when we try to add or delete
a rpwwn to the lunmask config which is not zoned to this port.  Check if the
FCS rport is not NULL before de-referencing it.

Signed-off-by: Krishna Gudipati <kgudipat@brocade.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>