[libata] ahci: Fix warning: comparison between 'enum <anonymous>' and 'enum <anonymous>'

The below patch casts ATA_MAX_QUEUE to int because GCC will
give a warning message about the two different enum blocks:
  CC      drivers/ata/ahci.o
drivers/ata/ahci.c: In function 'ahci_init_one':
drivers/ata/ahci.c:1045:2: warning: comparison between 'enum <anonymous>' and 'enum <anonymous>'

Signed-off-by: Justin P. Mattock <justinmattock@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/ahci.c

@@ -1042,7 +1042,7 @@ static int ahci_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 
 	VPRINTK("ENTER\n");
 
-	WARN_ON(ATA_MAX_QUEUE > AHCI_MAX_CMDS);
+	WARN_ON((int)ATA_MAX_QUEUE > AHCI_MAX_CMDS);
 
 	if (!printed_version++)
 		dev_printk(KERN_DEBUG, &pdev->dev, "version " DRV_VERSION "\n");