ACPI: video: check for error while searching for backlight device parent

If acpi_get_parent() called in acpi_video_dev_register_backlight()
fails, for example, because acpi_ut_acquire_mutex() fails inside
acpi_get_parent), this can lead to incorrect (uninitialized)
acpi_parent handle being passed to acpi_get_pci_dev() for detecting
the parent pci device.

Check acpi_get_parent() result and set parent device only in case of success.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 9661e92 ("acpi: tie ACPI backlight devices to PCI devices if possible")
Signed-off-by: Nikita Kiryushin <kiryushin@ancud.ru>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: nkiryushin

drivers/acpi/acpi_video.c

@@ -1717,12 +1717,12 @@ static void acpi_video_dev_register_backlight(struct acpi_video_device *device)
 		return;
 	count++;
 
-	acpi_get_parent(device->dev->handle, &acpi_parent);
-
-	pdev = acpi_get_pci_dev(acpi_parent);
-	if (pdev) {
-		parent = &pdev->dev;
-		pci_dev_put(pdev);
+	if (ACPI_SUCCESS(acpi_get_parent(device->dev->handle, &acpi_parent))) {
+		pdev = acpi_get_pci_dev(acpi_parent);
+		if (pdev) {
+			parent = &pdev->dev;
+			pci_dev_put(pdev);
+		}
 	}
 
 	memset(&props, 0, sizeof(struct backlight_properties));