sysupgrade: do not kill any processes in failsafe

sysugrade killed the lock causing failsafe to stop

Signed-off-by: Alexander Couzens <lynxis@fe80.eu>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39318 3c298f89-4303-0410-b956-a3cf2f4a3e73