kernel: fix race condition between compile_kernelmodules and shared_workdir

kernel: fix race condition between compile_kernelmodules and shared_workdir

Fixes https://bugzilla.yoctoproject.org/show_bug.cgi?id=8127 which causes
[ 1225.089323] 8189es: Unknown symbol cfg80211_scan_done (err -22)
[ 1225.095916] 8189es: no symbol version for cfg80211_remain_on_channel_expired
when loading external compiled 8189es module.

Signed-off-by: Jens Rehsack <sno@netbsd.org>
Signed-off-by: Ross Burton <ross.burton@intel.com>