ACPI / fan: fix fan driver compile error when CONFIG_PM_SLEEP is undefined

The ACPI fan driver defines acpi_fan_suspend() and acpi_fan_resume()
when CONFIG_PM_SLEEP is defined. This results in the following compile
errors when CONFIG_PM_SLEEP is undefined:

drivers/acpi/fan.c:60:8: error: ‘acpi_fan_suspend’ undeclared here (not in a function)
drivers/acpi/fan.c:60:8: error: ‘acpi_fan_resume’ undeclared here (not in a function)
Signed-off-by: Shuah Khan <shuah.kh@samsung.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/fan.c

@@ -55,6 +55,9 @@ MODULE_DEVICE_TABLE(acpi, fan_device_ids);
 #ifdef CONFIG_PM_SLEEP
 static int acpi_fan_suspend(struct device *dev);
 static int acpi_fan_resume(struct device *dev);
+#else
+#define acpi_fan_suspend NULL
+#define acpi_fan_resume NULL
 #endif
 static SIMPLE_DEV_PM_OPS(acpi_fan_pm, acpi_fan_suspend, acpi_fan_resume);