mlxsw: spectrum_span: Use a more fitting error code

ENOENT is suitable when an item is looked for in a collection and can't
be found. The failure here is actually a depletion of a resource, where
ENOBUFS is the more fitting error code.
Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -924,7 +924,7 @@ int mlxsw_sp_span_mirror_add(struct mlxsw_sp_port *from,
 
 	span_entry = mlxsw_sp_span_entry_get(mlxsw_sp, to_dev, ops, sparms);
 	if (!span_entry)
-		return -ENOENT;
+		return -ENOBUFS;
 
 	netdev_dbg(from->dev, "Adding inspected port to SPAN entry %d\n",
 		   span_entry->id);