scsi: zfcp: more fitting constant for fc_ct_hdr.ct_reason on port scan response

v2.6.33 commit dbf5dfe9 ("[SCSI] zfcp: Use common code definitions for
FC CT structs") replaced own definitions with common code definitions.
While FC_BA_RJT_UNABLE happens to be defined with the same value 9 as
FC_FS_RJT_UNABL and thus also works, here we should use the latter from
fc_gs.h.
See also its use in libfc's fc_disc_gpn_ft_resp().

Signed-off-by: Steffen Maier <maier@linux.vnet.ibm.com>
Reviewed-by: Benjamin Block <bblock@linux.vnet.ibm.com>
Signed-off-by: Benjamin Block <bblock@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>