[SCSI] mpt2sas: Check for NULL pointer before free_pages is added.

Added check before free_pages just to make sure ioc->scsi_lookup is not NULL.
Signed-off-by: Kashyap Desai <kashyap.desai@lsi.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

drivers/scsi/mpt2sas/mpt2sas_base.c

@@ -1919,7 +1919,10 @@ _base_release_memory_pools(struct MPT2SAS_ADAPTER *ioc)
 		    ioc->config_page, ioc->config_page_dma);
 	}
 
+	if (ioc->scsi_lookup) {
 		free_pages((ulong)ioc->scsi_lookup, ioc->scsi_lookup_pages);
+		ioc->scsi_lookup = NULL;
+	}
 	kfree(ioc->hpr_lookup);
 	kfree(ioc->internal_lookup);
 }