scsi: qla2xxx: Change a stack variable into a static const variable

Make qla2x00_get_host_fabric_name() slightly faster by changing a stack
array into a static array. Declare that array const now that the
wwn_to_u64() argument pointer has been declared const.

Cc: Himanshu Madhani <hmadhani@marvell.com>
Cc: Giridhar Malavali <gmalavali@marvell.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Acked-by: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>