openocd: libusb patch: append rather than override LDFLAGS

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/openocd/openocd-0001-fix-cross-compilation-host-libsub-was-used-before.patch

@@ -23,7 +23,7 @@ index dfa1e8f..cfe2218 100644
 +  dnl check for libusb
 +  PKG_CHECK_MODULES(LIBUSB, libusb >= 0.1.11)
 +  CFLAGS="$CFLAGS $LIBUSB_CFLAGS"
-+  LDFLAGS="$LFFLAGS $LIBUSB_LDFLAGS"
++  LDFLAGS="$LDFLAGS $LIBUSB_LDFLAGS"
 +  LIBS="$LIBS $LIBUSB_LIBS"
    build_usb=yes
  fi