i40iw: Do not set self-referencing pointer to NULL after kfree

In i40iw_free_virt_mem(), do not set mem->va to NULL
after freeing it as mem->va is a self-referencing pointer
to mem.

Fixes: 4e9042e6 ("i40iw: add hw and utils files")
Reported-by: NStefan Assmann <sassmann@redhat.com>
Signed-off-by: NMustafa Ismail <mustafa.ismail@intel.com>
Signed-off-by: NShiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: NDoug Ledford <dledford@redhat.com>

drivers/infiniband/hw/i40iw/i40iw_utils.c

@@ -673,8 +673,11 @@ enum i40iw_status_code i40iw_free_virt_mem(struct i40iw_hw *hw,
 {
 	if (!mem)
 		return I40IW_ERR_PARAM;
+	/*
+	 * mem->va points to the parent of mem, so both mem and mem->va
+	 * can not be touched once mem->va is freed
+	 */
 	kfree(mem->va);
-	mem->va = NULL;
 	return 0;
 }