[rdk-b][common][bsp][Refactor kernel sync script from Openwrt]

[Description]
Refactor kernel sync script from Openwrt

[Release-log]
N/A

diff --git a/mtk_scripts/filogic-sync-openwrt-linux.sh b/mtk_scripts/filogic-sync-openwrt-linux.sh
index efbd39c..a3b8fad 100755
--- a/mtk_scripts/filogic-sync-openwrt-linux.sh
+++ b/mtk_scripts/filogic-sync-openwrt-linux.sh
@@ -83,7 +83,7 @@
 #end
 
 #update kernel version
-ver=`grep "LINUX_KERNEL_HASH-5" openwrt/include/kernel-version.mk | cut -c 19-25`
+ver=`grep "LINUX_KERNEL_HASH-5" openwrt/include/kernel-5.4 | cut -c 19-25`
 sed -i 's/LINUX_VERSION ?=.*/LINUX_VERSION ?= "'${ver}'"/g' meta-filogic/recipes-kernel/linux/linux-mediatek_5.4.bb
 #end