lowmemorykiller: Don't count reserve page twice

This is essentially revert of
dc41a1c6
Revert "lowmemorykiller: Don't count reserve page twice"

We need to resolve double accounting of the reserve
pages. Lastly, we have reverted this suspecting this
as culprit of some issue. But the nature of this patch
is cleaner and solving real issue of mis-accounting.

Change-Id: I29debaa1bc05703205b323b458f2dfe2938fdfa9
Signed-off-by: Chintan Pandya <cpandya@codeaurora.org>