sys_power: whitelist kernel 3.18 watermark warning.

BUG=chrome-os-partner:52275
TEST=run power_Resume on chell with external display connected.  See
that while WARN_ON(!wm_changed) occurred test still passed and produced
perf results.

Change-Id: I64fac7d0a1e9de04649193956c5d9ddbd606ed58
Reviewed-on: https://chromium-review.googlesource.com/338650
Commit-Ready: Todd Broch <tbroch@chromium.org>
Tested-by: Todd Broch <tbroch@chromium.org>
Reviewed-by: Benson Leung <bleung@chromium.org>
(cherry picked from commit 34e1294ee845aa172f6b4901b9628f85a7983928)
Reviewed-on: https://chromium-review.googlesource.com/341180
Reviewed-by: Sameer Nanda <snanda@chromium.org>
Commit-Queue: Todd Broch <tbroch@chromium.org>
1 file changed