smcinvoke: Remove workqueue has sleeper

If invoke calls are made before any accept threads then
its possible that workqueue has sleeper will return false.
So CB failures are seen during TA loading.

Change-Id: Id3b3a1907456c59bd8d51355dbdcba30a5c1a79a
Signed-off-by: AnilKumar Chimata <anilc@codeaurora.org>