when using a local kernel deb, make sure this isnt set

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>

mk_mmc.sh

@@ -199,6 +199,7 @@ function dl_kernel_image {
    wget -c --directory-prefix=${DIR}/dl/${DIST} ${MIRROR}cross/v${KERNEL}/${CROSS_DEB_FILE}
   fi
  else
+  unset DI_BROKEN_USE_CROSS
   KERNEL=${DEB_FILE}
   #Remove all "\" from file name.
   ACTUAL_DEB_FILE=$(echo ${DEB_FILE} | sed 's!.*/!!' | grep linux-image)