net/mlx5: fix warning about copy length

[ upstream commit c19580fb8e9ad6f153d46f731ec7cd2050b3021b ]

Use RTE_PTR_ADD where copying to the offset of a field in a structure
holding multiple fields, to avoid compiler warnings with decorated
rte_memcpy.

Fixes: 16a7dbc ("net/mlx5: make flow modify action list thread safe")

Signed-off-by: Morten Brørup <mb@smartsharesystems.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>

drivers/net/mlx5/mlx5_flow_dv.c

@@ -5464,7 +5464,7 @@ flow_dv_modify_create_cb(void *tool_ctx, void *cb_ctx)
 				   "cannot allocate resource memory");
 		return NULL;
 	}
-	rte_memcpy(&entry->ft_type,
+	rte_memcpy(RTE_PTR_ADD(entry, offsetof(typeof(*entry), ft_type)),
 		   RTE_PTR_ADD(ref, offsetof(typeof(*ref), ft_type)),
 		   key_len + data_len);
 	if (entry->ft_type == MLX5DV_FLOW_TABLE_TYPE_FDB)