[openwrt/openwrt] bcm4908: fix calculation of new cferam index

[LEDE Commits]

rmilecki pushed a commit to openwrt/openwrt.git, branch openwrt-21.02:
https://git.openwrt.org/4607f55439c2a03154f71ba9d366cff8f52443d2

commit 4607f55439c2a03154f71ba9d366cff8f52443d2
Author: Sungbo Eo <mans0n at gorani.run>
AuthorDate: Sun Aug 1 22:17:04 2021 +0900

    bcm4908: fix calculation of new cferam index
    
    The arithmetic expansion fails when idx becomes a two digit number.
    Fix this by relying on expr command.
    
    root at OpenWrt:/# echo $(((028 + 0) % 1000))
    /bin/ash: arithmetic syntax error
    root at OpenWrt:/# echo $(($(expr 028 + 0) % 1000))
    28
    
    Fixes: a6a0b252baa6 ("bcm4908: add sysupgrade support")
    Signed-off-by: Sungbo Eo <mans0n at gorani.run>
    (cherry picked from commit f4323538501d58298f4df73a034a51375a477cfc)
---
 target/linux/bcm4908/base-files/lib/upgrade/platform.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/target/linux/bcm4908/base-files/lib/upgrade/platform.sh b/target/linux/bcm4908/base-files/lib/upgrade/platform.sh
index 8aca7119e4..ee43e3a713 100644
--- a/target/linux/bcm4908/base-files/lib/upgrade/platform.sh
+++ b/target/linux/bcm4908/base-files/lib/upgrade/platform.sh
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
 
-RAMFS_COPY_BIN="bcm4908img"
+RAMFS_COPY_BIN="bcm4908img expr"
 
 PART_NAME=firmware
 
@@ -129,7 +129,7 @@ platform_calc_new_cferam() {
 	umount $dir
 	rm -fr $dir
 
-	idx=$(((idx + inc) % 1000))
+	idx=$(($(expr $idx + $inc) % 1000))
 
 	echo $(printf "cferam.%03d" $idx)
 }