Fix compilation warnings

src/Makefile

@@ -6,7 +6,7 @@ BIN=0xFFFF
 #LIBS=`${HAVE_USB} && echo -- '-lusb'`
 LIBS=`if [ "${HAVE_USB}" = 1 ]; then echo '-lusb'; fi`
 CFLAGS+=-DVERSION=\"${VERSION}\" -Wall -I .
-CFLAGS+=-pedantic -std=c99 -DHAVE_USB=${HAVE_USB}
+CFLAGS+=-pedantic -std=c99 -DHAVE_USB=${HAVE_USB} -Wno-unused-result
 USBOBJ=../libusb/error.o ../libusb/usb.o ../libusb/descriptors.o
 USBOBJ+=../libusb/linux.o ## XXX not portable