dpaa2-switch: fix default return of dpaa2_switch_flower_parse_mirror_key

Clang static analysis reports this representative problem
dpaa2-switch-flower.c:616:24: warning: The right operand of '=='
  is a garbage value
  tmp->cfg.vlan_id == vlan) {
                   ^  ~~~~
vlan is set in dpaa2_switch_flower_parse_mirror_key(). However
this function can return success without setting vlan.  So
change the default return to -EOPNOTSUPP.

Fixes: 0f3faece ("dpaa2-switch: add VLAN based mirroring")
Signed-off-by: NTom Rix <trix@redhat.com>
Reviewed-by: NIoana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/dpaa2/dpaa2-switch-flower.c

@@ -532,6 +532,7 @@ static int dpaa2_switch_flower_parse_mirror_key(struct flow_cls_offload *cls,
 	struct flow_rule *rule = flow_cls_offload_flow_rule(cls);
 	struct flow_dissector *dissector = rule->match.dissector;
 	struct netlink_ext_ack *extack = cls->common.extack;
+	int ret = -EOPNOTSUPP;
 
 	if (dissector->used_keys &
 	    ~(BIT(FLOW_DISSECTOR_KEY_BASIC) |
@@ -561,9 +562,10 @@ static int dpaa2_switch_flower_parse_mirror_key(struct flow_cls_offload *cls,
 		}
 
 		*vlan = (u16)match.key->vlan_id;
+		ret = 0;
 	}
 
-	return 0;
+	return ret;
 }
 
 static int