scsi: mpt3sas: Fix kernel panic during drive powercycle test

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: f92363d123 ("[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>

drivers/scsi/mpt3sas/mpt3sas_scsih.c

@@ -3869,7 +3869,7 @@ _scsih_ublock_io_device(struct MPT3SAS_ADAPTER *ioc,
 
 	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)