thunderbolt: Add tb_switch_get()

Sometimes there is need for increasing reference count of a switch as
well. This also follows what we have for xdomains.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>

drivers/thunderbolt/tb.h

@@ -387,6 +387,13 @@ struct tb_switch *tb_switch_find_by_link_depth(struct tb *tb, u8 link,
 					       u8 depth);
 struct tb_switch *tb_switch_find_by_uuid(struct tb *tb, const uuid_t *uuid);
 
+static inline struct tb_switch *tb_switch_get(struct tb_switch *sw)
+{
+	if (sw)
+		get_device(&sw->dev);
+	return sw;
+}
+
 static inline void tb_switch_put(struct tb_switch *sw)
 {
 	put_device(&sw->dev);