UPSTREAM: staging: android: lowmemorykiller: neglect swap cached pages in other_file

(cherry picked from commit 058dbde9)

With ZRAM enabled it is observed that lowmemory killer
doesn't trigger properly. swap cached pages are
accounted in NR_FILE, and lowmemorykiller considers
this as reclaimable and adds to other_file. But these
pages can't be reclaimed unless lowmemorykiller triggers.
So subtract swap pages from other_file.

Signed-off-by: Vinayak Menon <vinayakm.list@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Change-Id: Id1321ebca9dbfe69333d5001bc2db9f6764654ea