only write new buildnumber when actually download a new build

chip-update-firmware.sh

@@ -13,6 +13,7 @@ function require_directory {
 
 function cache_download {
   if [[ ! -f "${1}/${2}" ]]; then
+    echo "$BUILD" > ${FW_IMAGE_DIR}/build
     
     wget -P "${FW_IMAGE_DIR}" "${LATEST_URL}images/${2}" ||
       exit 1
@@ -56,7 +57,6 @@ if [[ -z "${BUILD}" ]]; then
 fi
 
 require_directory "${FW_IMAGE_DIR}"
-echo "$BUILD" > ${FW_IMAGE_DIR}/build
 cache_download "${FW_IMAGE_DIR}" rootfs.ubi
 cache_download "${FW_IMAGE_DIR}" sun5i-r8-chip.dtb
 cache_download "${FW_IMAGE_DIR}" sunxi-spl.bin