mpt3sas: A correction in unmap_resources

BugLink: http://bugs.launchpad.net/bugs/1512221

It might happen that we try to free an already freed pointer.
Reported-by: Maurizio Lombardi <mlombard@redhat.com>
Signed-off-by: Tomas Henzl <thenzl@redhat.com>
Acked-by: Chaitra P B <chaitra.basappa@avagotech.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
(cherry picked from commit 5f985d88)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/scsi/mpt3sas/mpt3sas_base.c

@@ -2020,8 +2020,10 @@ mpt3sas_base_unmap_resources(struct MPT3SAS_ADAPTER *ioc)
 	_base_free_irq(ioc);
 	_base_disable_msix(ioc);
 
-	if (ioc->msix96_vector)
+	if (ioc->msix96_vector) {
 		kfree(ioc->replyPostRegisterIndex);
+		ioc->replyPostRegisterIndex = NULL;
+	}
 
 	if (ioc->chip_phys) {
 		iounmap(ioc->chip);