ata: libata-core: Do not try to set sleeping devices to standby

In ata ata_dev_power_set_standby(), check that the target device is not
sleeping. If it is, there is no need to do anything.

Fixes: aa3998db ("ata: libata-scsi: Disable scsi device manage_system_start_stop")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Niklas Cassel <cassel@kernel.org>

drivers/ata/libata-core.c

@@ -2017,6 +2017,10 @@ void ata_dev_power_set_standby(struct ata_device *dev)
 	struct ata_taskfile tf;
 	unsigned int err_mask;
 
+	/* If the device is already sleeping, do nothing. */
+	if (dev->flags & ATA_DFLAG_SLEEPING)
+		return;
+
 	/*
 	 * Some odd clown BIOSes issue spindown on power off (ACPI S4 or S5)
 	 * causing some drives to spin up and down again. For these, do nothing