sata_sil24: sil24_interrupt() micro-optimisation

sil24_interrupt() loads host->ports[i] into a local variable,
validates it, and then loads the value again in the call to
sil24_host_intr(). This patch replaces the second load by a
reference to the local variable.

This is safe since no side-effects have occurred since the
initial load. It also improves readability since it makes
it clear that the parameter to sil24_host_intr() is the same
value which was just validated.
Signed-off-by: Mikael Pettersson <mikpe@it.uu.se>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/sata_sil24.c

@@ -888,7 +888,7 @@ static irqreturn_t sil24_interrupt(int irq, void *dev_instance)
 		if (status & (1 << i)) {
 			struct ata_port *ap = host->ports[i];
 			if (ap && !(ap->flags & ATA_FLAG_DISABLED)) {
-				sil24_host_intr(host->ports[i]);
+				sil24_host_intr(ap);
 				handled++;
 			} else
 				printk(KERN_ERR DRV_NAME