fix "depend" target in npe directory

Signed-off-by: Michael Schwingen <michael@schwingen.org>

arch/arm/cpu/ixp/npe/Makefile

@@ -27,6 +27,7 @@ LIB := $(obj)libnpe.o
 
 LOCAL_CFLAGS  += -I$(TOPDIR)/arch/arm/cpu/ixp/npe/include -DCONFIG_IXP425_COMPONENT_ETHDB -D__linux
 CFLAGS  += $(LOCAL_CFLAGS)
+CPPFLAGS  += $(LOCAL_CFLAGS) # needed for depend
 HOSTCFLAGS  += $(LOCAL_CFLAGS)
 
 COBJS-$(CONFIG_IXP4XX_NPE) := npe.o \