initscripts: use quotes for shell variable comparision

Helps to execute it with busybox shell

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 45ba0ca0)
Signed-off-by: Anuj Mittal <anuj.mittal@intel.com>