AHCI: Do not acquire ata_host::lock from single IRQ handler

There is no need to acquire ata_host::lock spinlock from
hardware context single IRQ interrupt handler since the
handler does not access host data that could be altered
by concurrent processors.

Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: linux-ide@vger.kernel.org

drivers/ata/libahci.c

@@ -1875,8 +1875,6 @@ static irqreturn_t ahci_single_irq_intr(int irq, void *dev_instance)
 
 	irq_masked = irq_stat & hpriv->port_map;
 
-	spin_lock(&host->lock);
-
 	for (i = 0; i < host->n_ports; i++) {
 		struct ata_port *ap;
 
@@ -1908,8 +1906,6 @@ static irqreturn_t ahci_single_irq_intr(int irq, void *dev_instance)
 	 */
 	writel(irq_stat, mmio + HOST_IRQ_STAT);
 
-	spin_unlock(&host->lock);
-
 	VPRINTK("EXIT\n");
 
 	return handled ? IRQ_WAKE_THREAD : IRQ_NONE;