scsi: lpfc: Fix premature re-enabling of interrupts in lpfc_sli_host_down

Use of spin_lock_irq may re-enable interrupts prematurely.

Convert to spin_lock. Note: code is under the phba->hba_lock which has been
locked with irqsave.

Link: https://lore.kernel.org/r/20190922035906.10977-3-jsmart2021@gmail.com
Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>