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>