mlxsw: spectrum: mr: Make the function mlxsw_sp_mr_dev_vif_lookup static

The function is only used internally in spectrum_mr.c and is not declared
in the header file, thus make it static.

Cleans up sparse warning:
symbol 'mlxsw_sp_mr_dev_vif_lookup' was not declared. Should it be static?

Fixes: c011ec1bbfd6 ("mlxsw: spectrum: Add the multicast routing offloading logic")
Signed-off-by: Yotam Gigi <yotamg@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -768,7 +768,7 @@ void mlxsw_sp_mr_vif_del(struct mlxsw_sp_mr_table *mr_table, vifi_t vif_index)
 	mlxsw_sp_mr_vif_unresolve(mr_table, NULL, mr_vif);
 }
 
-struct mlxsw_sp_mr_vif *
+static struct mlxsw_sp_mr_vif *
 mlxsw_sp_mr_dev_vif_lookup(struct mlxsw_sp_mr_table *mr_table,
 			   const struct net_device *dev)
 {