scsi: mpt3sas: Fix kernel panic during drive powercycle test

[ Upstream commit 0ee4ba13e09c9d9c1cb6abb59da8295d9952328b ]

While looping over shost's sdev list it is possible that one
of the drives is getting removed and its sas_target object is
freed but its sdev object remains intact.

Consequently, a kernel panic can occur while the driver is trying to access
the sas_address field of sas_target object without also checking the
sas_target object for NULL.

Link: https://lore.kernel.org/r/20211117104909.2069-1-sreekanth.reddy@broadcom.com
Fixes: f92363d12359 ("[SCSI] mpt3sas: add new driver supporting 12GB SAS")
Signed-off-by: Sreekanth Reddy <sreekanth.reddy@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
diff --git a/drivers/scsi/mpt3sas/mpt3sas_scsih.c b/drivers/scsi/mpt3sas/mpt3sas_scsih.c
index 58876b8..8063b97 100644
--- a/drivers/scsi/mpt3sas/mpt3sas_scsih.c
+++ b/drivers/scsi/mpt3sas/mpt3sas_scsih.c
@@ -2927,7 +2927,7 @@
 
 	shost_for_each_device(sdev, ioc->shost) {
 		sas_device_priv_data = sdev->hostdata;
-		if (!sas_device_priv_data)
+		if (!sas_device_priv_data || !sas_device_priv_data->sas_target)
 			continue;
 		if (sas_device_priv_data->sas_target->sas_address
 		    != sas_address)