x86/pci/intel_mid_pci: Use proper constants for irq polarity

polarity = 0 means active high. Not really intuitive, so people add
comments to it instead of just using a self explaining constant.

Use the IOAPIC_POL_ constants and get rid of those horrible to read
tail comments.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>

arch/x86/pci/intel_mid_pci.c

@@ -220,7 +220,7 @@ static int intel_mid_pci_irq_enable(struct pci_dev *dev)
 
 	switch (intel_mid_identify_cpu()) {
 	case INTEL_MID_CPU_CHIP_TANGIER:
-		polarity = 0; /* active high */
+		polarity = IOAPIC_POL_HIGH;
 
 		/* Special treatment for IRQ0 */
 		if (dev->irq == 0) {
@@ -235,7 +235,7 @@ static int intel_mid_pci_irq_enable(struct pci_dev *dev)
 		}
 		break;
 	default:
-		polarity = 1; /* active low */
+		polarity = IOAPIC_POL_LOW;
 		break;
 	}