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/ixp4xx_npe.c b/arch/arm/mach-ixp4xx/ixp4xx_npe.c
index 47ac69c..e8bb257 100644
--- a/arch/arm/mach-ixp4xx/ixp4xx_npe.c
+++ b/arch/arm/mach-ixp4xx/ixp4xx_npe.c
@@ -665,7 +665,7 @@
 }
 
 
-struct npe *npe_request(int id)
+struct npe *npe_request(unsigned id)
 {
 	if (id < NPE_COUNT)
 		if (npe_tab[id].valid)