device: fix error in generating BUILD_NUMBER

echo $((08/4))
bash: 08: value too great for base (error token is "08")

Signed-off-by: hmz007 <hmz007@gmail.com>

build.sh

@@ -198,7 +198,7 @@ function build_kernel() {
 }
 
 function build_android() {
-	true ${BUILD_NUMBER:=$(date +"6%y%m%d")$(($(date +"%H")/4))}
+	true ${BUILD_NUMBER:=$(date +"6%y%m%d")$(($(date +"%k")/4))}
 	export BUILD_NUMBER
 
 	FA_RunCmd lunch ${PRODUCT}-${VARIANT}