irqchip: crossbar: Dont use '0' to mark reserved interrupts

Today '0' is actually reserved, but may not be the same in the future.

So, use a flag to mark the GIC interrupts that are reserved.
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Sricharan R <r.sricharan@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Link: https://lkml.kernel.org/r/1403766634-18543-2-git-send-email-r.sricharan@ti.comSigned-off-by: Jason Cooper <jason@lakedaemon.net>

drivers/irqchip/irq-crossbar.c

@@ -17,6 +17,7 @@
 #include <linux/irqchip/arm-gic.h>
 
 #define IRQ_FREE	-1
+#define IRQ_RESERVED	-2
 #define GIC_IRQ_START	32
 
 /*
@@ -139,7 +140,7 @@ static int __init crossbar_of_init(struct device_node *node)
 				pr_err("Invalid reserved entry\n");
 				goto err3;
 			}
-			cb->irq_map[entry] = 0;
+			cb->irq_map[entry] = IRQ_RESERVED;
 		}
 	}
 
@@ -170,7 +171,7 @@ static int __init crossbar_of_init(struct device_node *node)
 	 * reserved irqs. so find and store the offsets once.
 	 */
 	for (i = 0; i < max; i++) {
-		if (!cb->irq_map[i])
+		if (cb->irq_map[i] == IRQ_RESERVED)
 			continue;
 
 		cb->register_offsets[i] = reserved;