mm: process_reclaim: skip target_vma

Skip using target_vma for address space reclaim. Shared pages
are not reclaimed by this interface and thus there isn't a need
to perform targeted reclaim.

Change-Id: I17cc0452c1179786ac64f0dd1ee81b2b71bb7caa
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>