pinctrl: th1520: Convert thp->mutex to guarded mutex

Convert th1520_pinctrl_dt_node_to_map() to use guarded mutex for
thp->mutex.

Suggested-by: Linus Walleij <[e-mail]>
Signed-off-by: Drew Fustini <[e-mail]>
Link: https://lore.kernel.org/[e-mail]
Signed-off-by: Linus Walleij <[e-mail]>

drivers/pinctrl/pinctrl-th1520.c

···
 		return -ENOMEM;
 
 	nmaps = 0;
-	mutex_lock(&thp->mutex);
+	guard(mutex)(&thp->mutex);
 	for_each_available_child_of_node(np, child) {
 		unsigned int rollback = nmaps;
 		enum th1520_muxtype muxtype;
···
 
 	*maps = map;
 	*num_maps = nmaps;
-	mutex_unlock(&thp->mutex);
 	return 0;
 
 free_configs:
···
 put_child:
 	of_node_put(child);
 	th1520_pinctrl_dt_free_map(pctldev, map, nmaps);
-	mutex_unlock(&thp->mutex);
 	return ret;
 }