defconfig: disable slub debug on sdm660

Disable default enablement of slub debug on sdm660
debug defconfig to prevent skb allocation failure
due to increase in order of allocation.

Change-Id: If63822a5abf3b297a34b95e5e5f973556631bd68
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>