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: f92363d1 ("[SCSI] mpt3sas: add new driver supporting 12GB SAS")
Signed-off-by: NSreekanth Reddy <sreekanth.reddy@broadcom.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>