net: marvell: prestera: fix incorrect return of port_find

In case, when some ports is in list and we don't find requested - we
return last iterator state and not return NULL as expected.

Fixes: 501ef306 ("net: marvell: prestera: Add driver for Prestera family ASIC devices")
Signed-off-by: Yevhen Orlov <yevhen.orlov@plvision.eu>
Link: https://lore.kernel.org/r/20211216170736.8851-1-yevhen.orlov@plvision.euSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/marvell/prestera/prestera_main.c

@@ -54,12 +54,14 @@ int prestera_port_pvid_set(struct prestera_port *port, u16 vid)
 struct prestera_port *prestera_port_find_by_hwid(struct prestera_switch *sw,
 						 u32 dev_id, u32 hw_id)
 {
-	struct prestera_port *port = NULL;
+	struct prestera_port *port = NULL, *tmp;
 
 	read_lock(&sw->port_list_lock);
-	list_for_each_entry(port, &sw->port_list, list) {
-		if (port->dev_id == dev_id && port->hw_id == hw_id)
+	list_for_each_entry(tmp, &sw->port_list, list) {
+		if (tmp->dev_id == dev_id && tmp->hw_id == hw_id) {
+			port = tmp;
 			break;
+		}
 	}
 	read_unlock(&sw->port_list_lock);
 
@@ -68,12 +70,14 @@ struct prestera_port *prestera_port_find_by_hwid(struct prestera_switch *sw,
 
 struct prestera_port *prestera_find_port(struct prestera_switch *sw, u32 id)
 {
-	struct prestera_port *port = NULL;
+	struct prestera_port *port = NULL, *tmp;
 
 	read_lock(&sw->port_list_lock);
-	list_for_each_entry(port, &sw->port_list, list) {
-		if (port->id == id)
+	list_for_each_entry(tmp, &sw->port_list, list) {
+		if (tmp->id == id) {
+			port = tmp;
 			break;
+		}
 	}
 	read_unlock(&sw->port_list_lock);