mm: move zone watermark accesses behind an accessor

This is a preparation patch only, no functional change.

Link: http://lkml.kernel.org/r/20181123114528.28802-3-mgorman@techsingularity.net


Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Zi Yan <zi.yan@cs.rutgers.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Change-Id: Iccef5f02348ab59d75cbbe2b48f40017391b88b1
Git-commit: a921444382b49cc7fdeca3fba3e278bc09484a27
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git


[vinmenon@codeaurora.org: trivial merge conflict fixes]
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>