tty: simplify tty_dev_name_to_number() using guard(mutex)

In tty_dev_name_to_number(), a guard can help to make the code easier to
follow. Especially how 0 is returned in the successful case. So use a
guard there.
Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20240805102046.307511-2-jirislaby@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_io.c

@@ -350,22 +350,19 @@ int tty_dev_name_to_number(const char *name, dev_t *number)
 		return ret;
 
 	prefix_length = str - name;
-	mutex_lock(&tty_mutex);
+
+	guard(mutex)(&tty_mutex);
 
 	list_for_each_entry(p, &tty_drivers, tty_drivers)
 		if (prefix_length == strlen(p->name) && strncmp(name,
 					p->name, prefix_length) == 0) {
 			if (index < p->num) {
 				*number = MKDEV(p->major, p->minor_start + index);
-				goto out;
+				return 0;
 			}
 		}
 
-	/* if here then driver wasn't found */
-	ret = -ENODEV;
-out:
-	mutex_unlock(&tty_mutex);
-	return ret;
+	return -ENODEV;
 }
 EXPORT_SYMBOL_GPL(tty_dev_name_to_number);