ACPI: processor: idle: Check acpi_fetch_acpi_dev() return value

The return value of acpi_fetch_acpi_dev() could be NULL, which would
cause a NULL pointer dereference to occur in acpi_device_hid().
Signed-off-by: Li Zhong <floridsleeves@gmail.com>
[ rjw: Subject and changelog edits, added empty line after if () ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/processor_idle.c

@@ -1134,6 +1134,9 @@ static int acpi_processor_get_lpi_info(struct acpi_processor *pr)
 	status = acpi_get_parent(handle, &pr_ahandle);
 	while (ACPI_SUCCESS(status)) {
 		d = acpi_fetch_acpi_dev(pr_ahandle);
+		if (!d)
+			break;
+
 		handle = pr_ahandle;
 
 		if (strcmp(acpi_device_hid(d), ACPI_PROCESSOR_CONTAINER_HID))