nfp: flower: Fix a potential leak in nfp_tunnel_add_shared_mac()

ida_simple_get() returns an id between min (0) and max (NFP_MAX_MAC_INDEX)
inclusive.
So NFP_MAX_MAC_INDEX (0xff) is a valid id.

In order for the error handling path to work correctly, the 'invalid'
value for 'ida_idx' should not be in the 0..NFP_MAX_MAC_INDEX range,
inclusive.

So set it to -1.

Fixes: 20cce886 ("nfp: flower: enable MAC address sharing for offloadable devs")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20220218131535.100258-1-simon.horman@corigine.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/netronome/nfp/flower/tunnel_conf.c

@@ -922,8 +922,8 @@ nfp_tunnel_add_shared_mac(struct nfp_app *app, struct net_device *netdev,
 			  int port, bool mod)
 {
 	struct nfp_flower_priv *priv = app->priv;
-	int ida_idx = NFP_MAX_MAC_INDEX, err;
 	struct nfp_tun_offloaded_mac *entry;
+	int ida_idx = -1, err;
 	u16 nfp_mac_idx = 0;
 
 	entry = nfp_tunnel_lookup_offloaded_macs(app, netdev->dev_addr);
@@ -997,7 +997,7 @@ nfp_tunnel_add_shared_mac(struct nfp_app *app, struct net_device *netdev,
 err_free_entry:
 	kfree(entry);
 err_free_ida:
-	if (ida_idx != NFP_MAX_MAC_INDEX)
+	if (ida_idx != -1)
 		ida_simple_remove(&priv->tun.mac_off_ids, ida_idx);
 
 	return err;