[][openwrt][common][fstool][Fix fstool build fail w/ glibc]

[Description]
Fix fstool build fail w/ glibc

[Release-log]
N/A

Change-Id: I93d7ecea0ff23de07d27cb1e0d06b105805d625b
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/6359178
1 file changed