scsi: lpfc: Fix crash after handling a pci error

Injecting EEH on a 32GB card is causing kernel oops

The pci error handler is doing an IO flush and the offline code is also
doing an IO flush. When the 1st flush is complete the hdwq is destroyed
(freed), yet the second flush accesses the hdwq and crashes.

Added a check in lpfc_sli4_fush_io_rings to check both the HBA_IOQ_FLUSH
flag and the hdwq pointer to see if it is already set and not already
freed.

Link: https://lore.kernel.org/r/20200322181304.37655-6-jsmart2021@gmail.com
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>