mlxsw: spectrum_mr: Use flexible-array member instead of zero-length array

Suppresses the following coccinelle warning:

drivers/net/ethernet/mellanox/mlxsw/spectrum_mr.c:18:15-19: WARNING use flexible-array member instead
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/spectrum_mr.c

@@ -15,7 +15,7 @@ struct mlxsw_sp_mr {
 	struct list_head table_list;
 	struct mutex table_list_lock; /* Protects table_list */
 #define MLXSW_SP_MR_ROUTES_COUNTER_UPDATE_INTERVAL 5000 /* ms */
-	unsigned long priv[0];
+	unsigned long priv[];
 	/* priv has to be always the last item */
 };