ACPI: Do not prepare for hibernation in acpi_shutdown

Since we are now explicitly calling hibernation_ops->prepare() before
hibernation_ops->enter() in hibernation_platform_enter() (defined in
kernel/power/disk.c), ACPI should not call acpi_sleep_prepare(ACPI_STATE_S4)
from acpi_shutdown().

Signed-off-by: Rafael J. Wysocki <[e-mail]>
Acked-by: Pavel Machek <[e-mail]>
Cc: Len Brown <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/acpi/sleep/poweroff.c

···
 	case SYSTEM_POWER_OFF:
 		/* Prepare to power off the system */
 		return acpi_sleep_prepare(ACPI_STATE_S5);
-	case SYSTEM_SUSPEND_DISK:
-		/* Prepare to suspend the system to disk */
-		return acpi_sleep_prepare(ACPI_STATE_S4);
 	default:
 		return 0;
 	}