IB/hfi1: Do not destroy link_wq when the device is shut down

The workqueue link_wq should only be destroyed when the hfi1 driver is
unloaded, not when the device is shut down.

Fixes: 71d47008 ("IB/hfi1: Create workqueue for link events")
Link: https://lore.kernel.org/r/20200623204053.107638.70315.stgit@awfm-01.aw.intel.com
Cc: <stable@vger.kernel.org>
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Kaike Wan <kaike.wan@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/hw/hfi1/init.c

@@ -846,6 +846,10 @@ static void destroy_workqueues(struct hfi1_devdata *dd)
 			destroy_workqueue(ppd->hfi1_wq);
 			ppd->hfi1_wq = NULL;
 		}
+		if (ppd->link_wq) {
+			destroy_workqueue(ppd->link_wq);
+			ppd->link_wq = NULL;
+		}
 	}
 }
 
@@ -1122,14 +1126,10 @@ static void shutdown_device(struct hfi1_devdata *dd)
 		 * We can't count on interrupts since we are stopping.
 		 */
 		hfi1_quiet_serdes(ppd);
-
 		if (ppd->hfi1_wq)
 			flush_workqueue(ppd->hfi1_wq);
-		if (ppd->link_wq) {
+		if (ppd->link_wq)
 			flush_workqueue(ppd->link_wq);
-			destroy_workqueue(ppd->link_wq);
-			ppd->link_wq = NULL;
-		}
 	}
 	sdma_exit(dd);
 }