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

The ACPI SBS driver defines acpi_sbs_resume() when CONFIG_PM_SLEEP is
defined. This results in the following compile error when CONFIG_PM_SLEEP
is undefined:

  CC [M]  drivers/acpi/sbs.o
drivers/acpi/sbs.c:674:8: error: ‘acpi_sbs_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/sbs.c

@@ -668,6 +668,8 @@ static int acpi_sbs_resume(struct device *dev)
 	acpi_sbs_callback(sbs);
 	return 0;
 }
+#else
+#define acpi_sbs_resume NULL
 #endif
 
 static SIMPLE_DEV_PM_OPS(acpi_sbs_pm, NULL, acpi_sbs_resume);