net: ethernet: mtk_eth_soc: fix flow block refcounting logic

Since we call flow_block_cb_decref on FLOW_BLOCK_UNBIND, we also need to
call flow_block_cb_incref for a newly allocated cb.
Also fix the accidentally inverted refcount check on unbind.

Fixes: 502e84e2 ("net: ethernet: mtk_eth_soc: add flow offloading support")
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Link: https://lore.kernel.org/r/20230330120840.52079-1-nbd@nbd.nameSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mediatek/mtk_ppe_offload.c

@@ -576,6 +576,7 @@ mtk_eth_setup_tc_block(struct net_device *dev, struct flow_block_offload *f)
 		if (IS_ERR(block_cb))
 			return PTR_ERR(block_cb);
 
+		flow_block_cb_incref(block_cb);
 		flow_block_cb_add(block_cb, f);
 		list_add_tail(&block_cb->driver_list, &block_cb_list);
 		return 0;
@@ -584,7 +585,7 @@ mtk_eth_setup_tc_block(struct net_device *dev, struct flow_block_offload *f)
 		if (!block_cb)
 			return -ENOENT;
 
-		if (flow_block_cb_decref(block_cb)) {
+		if (!flow_block_cb_decref(block_cb)) {
 			flow_block_cb_remove(block_cb, f);
 			list_del(&block_cb->driver_list);
 		}