mm: process_reclaim: fix reclaim skip on low efficiency

The logic used to skip reclaim on low efficiency results
in process reclaim not triggering at all. Fix it by
properly handling the skip_reclaim atomic variable.

Change-Id: I119097bb9b1baf8f3e8d4afa0a6dc2c30c0de6e7
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>