ACPI button: don't try to use a non-existent lid device

If a call comes in to check the lid state but there's no lid device
present, we should return -ENODEV.
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/acpi/button.c

@@ -251,6 +251,9 @@ int acpi_lid_open(void)
 	acpi_status status;
 	unsigned long long state;
 
+	if (!lid_device)
+		return -ENODEV;
+
 	status = acpi_evaluate_integer(lid_device->handle, "_LID", NULL,
 				       &state);
 	if (ACPI_FAILURE(status))