scsi: lpfc: Fix setting IRQ affinity with an empty CPU mask

scsi: lpfc: Fix setting IRQ affinity with an empty CPU mask

Some systems are reporting the following log message during driver unload
or system shutdown:

  ics_rtas_set_affinity: No online cpus in the mask

A prior commit introduced the writing of an empty affinity mask in calls to
irq_set_affinity_hint() when disabling interrupts or when there are no
remaining online CPUs to service an eq interrupt. At least some ppc64
systems are checking whether affinity masks are empty or not.

Do not call irq_set_affinity_hint() with an empty CPU mask.

Fixes: dcaa21367938 ("scsi: lpfc: Change default IRQ model on AMD architectures")
Link: https://lore.kernel.org/r/20200828175332.130300-2-james.smart@broadcom.com
Cc: <stable@vger.kernel.org> # v5.5+
Co-developed-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>