net: stmmac: make tc_flow_parsers static

The tc_flow_parsers is not used outside of the driver, so
make it static to avoid the following sparse warning:

drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c:516:3: warning: symbol 'tc_flow_parsers' was not declared. Should it be static?
Signed-off-by: NBen Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_tc.c

@@ -510,7 +510,7 @@ static struct stmmac_flow_entry *tc_find_flow(struct stmmac_priv *priv,
 	return NULL;
 }
 
-struct {
+static struct {
 	int (*fn)(struct stmmac_priv *priv, struct flow_cls_offload *cls,
 		  struct stmmac_flow_entry *entry);
 } tc_flow_parsers[] = {