thunderbolt: Introduce tb_switch_depth()

This is useful helper to find out the depth of a connected router.
Convert the existing users to call this helper instead of open-coding.

No functional changes.
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

drivers/thunderbolt/tb.c

@@ -255,13 +255,13 @@ static int tb_enable_clx(struct tb_switch *sw)
 	 * this in the future to cover the whole topology if it turns
 	 * out to be beneficial.
 	 */
-	while (sw && sw->config.depth > 1)
+	while (sw && tb_switch_depth(sw) > 1)
 		sw = tb_switch_parent(sw);
 
 	if (!sw)
 		return 0;
 
-	if (sw->config.depth != 1)
+	if (tb_switch_depth(sw) != 1)
 		return 0;
 
 	/*

drivers/thunderbolt/tb.h

@@ -866,6 +866,15 @@ static inline struct tb_port *tb_switch_downstream_port(struct tb_switch *sw)
 	return tb_port_at(tb_route(sw), tb_switch_parent(sw));
 }
 
+/**
+ * tb_switch_depth() - Returns depth of the connected router
+ * @sw: Router
+ */
+static inline int tb_switch_depth(const struct tb_switch *sw)
+{
+	return sw->config.depth;
+}
+
 static inline bool tb_switch_is_light_ridge(const struct tb_switch *sw)
 {
 	return sw->config.vendor_id == PCI_VENDOR_ID_INTEL &&