libata-acpi: don't call sleeping function from invalid context

The problem is introduced by commit
664d080.

acpi_evaluate_integer is a sleeping function,
and it should not be called with spin_lock_irqsave.
https://bugzilla.redhat.com/show_bug.cgi?id=451399

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/libata-acpi.c

@@ -197,14 +197,17 @@ static void ata_acpi_handle_hotplug(struct ata_port *ap, struct ata_device *dev,
 		/* This device does not support hotplug */
 		return;
 
+	if (event == ACPI_NOTIFY_BUS_CHECK ||
+	    event == ACPI_NOTIFY_DEVICE_CHECK)
+		status = acpi_evaluate_integer(handle, "_STA", NULL, &sta);
+
 	spin_lock_irqsave(ap->lock, flags);
 
 	switch (event) {
 	case ACPI_NOTIFY_BUS_CHECK:
 	case ACPI_NOTIFY_DEVICE_CHECK:
 		ata_ehi_push_desc(ehi, "ACPI event");
 
-		status = acpi_evaluate_integer(handle, "_STA", NULL, &sta);
 		if (ACPI_FAILURE(status)) {
 			ata_port_printk(ap, KERN_ERR,
 				"acpi: failed to determine bay status (0x%x)\n",