openwrt: Disable libusb via --without-libusb

openwrt/bfgminer/Makefile

@@ -87,7 +87,7 @@ CONFIGURE_ARGS += --with-libmicrohttpd
 endif
 
 ifndef CONFIG_PACKAGE_$(PKG_NAME)_libusb
-CONFIGURE_ARGS += --disable-x6500 --disable-ztex
+CONFIGURE_ARGS += --without-libusb
 endif
 
 ifdef CONFIG_PACKAGE_$(PKG_NAME)_scrypt