IXP4xx: Ensure index is positive in irq_to_gpio() and npe_request().

The indexes were signed, so negatives were possible.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Krzysztof Hałasa <khc@pm.waw.pl>
diff --git a/arch/arm/mach-ixp4xx/common.c b/arch/arm/mach-ixp4xx/common.c
index cfd52fb..3bbf40f 100644
--- a/arch/arm/mach-ixp4xx/common.c
+++ b/arch/arm/mach-ixp4xx/common.c
@@ -117,7 +117,7 @@
 }
 EXPORT_SYMBOL(gpio_to_irq);
 
-int irq_to_gpio(int irq)
+int irq_to_gpio(unsigned int irq)
 {
 	int gpio = (irq < 32) ? irq2gpio[irq] : -EINVAL;