i40e: check that pointer VSI is not null before dereferencing it

Function i40e_find_vsi_from_id can potentially return null, hence
VSI may be null, so defensively check it is non-null before
dereferencing it to check the seid.

Fixes: e284fc2 ("i40e: Add and delete cloud filter")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Avinash Dayanand <avinash.dayanand@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_virtchnl_pf.c

@@ -3062,7 +3062,7 @@ static struct i40e_vsi *i40e_find_vsi_from_seid(struct i40e_vf *vf, u16 seid)
 
 	for (i = 0; i < vf->num_tc ; i++) {
 		vsi = i40e_find_vsi_from_id(pf, vf->ch[i].vsi_id);
-		if (vsi->seid == seid)
+		if (vsi && vsi->seid == seid)
 			return vsi;
 	}
 	return NULL;