scsi: lpfc: Fix EEH encountering oops with NVMe traffic

In testing, in a configuration with Redfish and native NVMe multipath when
an EEH is injected, a kernel oops is being encountered:

(unreliable)
lpfc_nvme_ls_req+0x328/0x720 [lpfc]
__nvme_fc_send_ls_req.constprop.13+0x1d8/0x3d0 [nvme_fc]
nvme_fc_create_association+0x224/0xd10 [nvme_fc]
nvme_fc_reset_ctrl_work+0x110/0x154 [nvme_fc]
process_one_work+0x304/0x5d

the NBMe transport is issuing a Disconnect LS request, which the driver
receives and tries to post but the work queue used by the driver is already
being torn down by the eeh.

Fix by validating the validity of the work queue before proceeding with the
LS transmit.

Link: https://lore.kernel.org/r/20210127221601.84878-1-jsmart2021@gmail.com
Reviewed-by: Ewan D. Milne <emilne@redhat.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>