pci: Add a constant for an invalid interrupt

Rather than using 0xff in the code, add a constant.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

drivers/pci/pci.c

@@ -269,7 +269,8 @@ int pci_hose_config_device(struct pci_controller *hose,
 	/* Disable interrupt line, if device says it wants to use interrupts */
 	pci_hose_read_config_byte(hose, dev, PCI_INTERRUPT_PIN, &pin);
 	if (pin != 0) {
-		pci_hose_write_config_byte(hose, dev, PCI_INTERRUPT_LINE, 0xff);
+		pci_hose_write_config_byte(hose, dev, PCI_INTERRUPT_LINE,
+					   PCI_INTERRUPT_LINE_DISABLE);
 	}
 
 	pci_hose_read_config_dword(hose, dev, PCI_COMMAND, &old_command);

include/pci.h

@@ -231,6 +231,8 @@
 #define PCI_MIN_GNT		0x3e	/* 8 bits */
 #define PCI_MAX_LAT		0x3f	/* 8 bits */
 
+#define PCI_INTERRUPT_LINE_DISABLE	0xff
+
 /* Header type 1 (PCI-to-PCI bridges) */
 #define PCI_PRIMARY_BUS		0x18	/* Primary bus number */
 #define PCI_SECONDARY_BUS	0x19	/* Secondary bus number */