Reapply "smalloc: smalloc() already clears memory, scalloc() need not do it again"

Reapply "smalloc: smalloc() already clears memory, scalloc() need not do it again"

This reverts commit eb7fe4550ff2a569d0d8c71de16a1ea1e1aaf0a5.

It turns out that each buffer is in fact cleared in smalloc_pool() when
it is called by smalloc(). So there is no need to clear the buffer a
second time in scalloc.

Signed-off-by: Vincent Fu <vincent.fu@samsung.com>