gpio: sysfs: extend the critical section for unregistering sysfs devices

Checking the gdev->mockdev pointer for NULL must be part of the critical
section.
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/gpio/gpiolib-sysfs.c

 // SPDX-License-Identifier: GPL-2.0
 
 #include <linux/bitops.h>
+#include <linux/cleanup.h>
 #include <linux/device.h>
 #include <linux/idr.h>
 #include <linux/init.h>
@@ -768,15 +769,15 @@ void gpiochip_sysfs_unregister(struct gpio_device *gdev)
 	struct gpio_desc *desc;
 	struct gpio_chip *chip = gdev->chip;
 
+	scoped_guard(mutex, &sysfs_lock) {
 		if (!gdev->mockdev)
 			return;
 
 		device_unregister(gdev->mockdev);
 
 		/* prevent further gpiod exports */
-	mutex_lock(&sysfs_lock);
 		gdev->mockdev = NULL;
-	mutex_unlock(&sysfs_lock);
+	}
 
 	/* unregister gpiod class devices owned by sysfs */
 	for_each_gpio_desc_with_flag(chip, desc, FLAG_SYSFS) {