Linaro -O3: disable -O3 for kernel/workqueue.c

It reports an array out of bounds warning and if I disable the
warning, I am seeing crashes related to workqueues.  Disable the
optimization as it appears to be incorrectly optimizing it.
Fix linaro -O3 warning (incorrect code hacked to be equivalent)
kernel/workqueue.c: avoid array subscript above array boundaries

Signed-off-by: Dennis Rassmann <showp1984@gmail.com>
Re-enable -O3 optimization for kernel/workqueue.c