proc: make oom adjustment files user read-only

Make oom_adj and oom_score_adj user read-only.

Bug: 19636629
Change-Id: I055bb172d5b4d3d856e25918f3c5de8edf31e4a3
Signed-off-by: Rom Lemarchand <romlem@google.com>
Git-commit: 7b4fff3195f2938fdb859471a8ffaa467ffc5167
Git-repo: https://android.googlesource.com/kernel/common.git


Signed-off-by: Ian Maund <imaund@codeaurora.org>