Fix property flag check when setting dpms
Fix property flag check when setting dpms

This bug had no affect, unless there was another property called "DPMS"
that was not a DRM_MODE_PROP_ENUM.

BUG=none
TEST=none

Change-Id: I1e0c9b59c0b1255e9d7c5f12dd168407bc420cf9
Reviewed-on: https://gerrit.chromium.org/gerrit/35650
Reviewed-by: Stéphane Marchesin <e16f69845633a0cf74affe1e5a677caa6296c937@chromium.org>
Commit-Ready: Daniel Kurtz <31914e832df1cd8e5daa417106c0c6f5297b27d7@chromium.org>
Reviewed-by: Daniel Kurtz <31914e832df1cd8e5daa417106c0c6f5297b27d7@chromium.org>
Tested-by: Daniel Kurtz <31914e832df1cd8e5daa417106c0c6f5297b27d7@chromium.org>

apxii/xf86-video-armsoc,commshare/xf86-video-armsoc,sbambrough/xf86-video-armsoc,freedesktop-unofficial-mirror/xorg__driver__xf86-video-armsoc,OtherCrashOverride/armsoc-hardkernel,mmind/xf86-video-armsoc,sbambrough/xf86-video-armsoc,xin3liang/xf86-video-armsoc,mdrjr/xf86-video-armsoc,mmind/xf86-video-armsoc,mdrjr/xf86-video-armsoc,freedesktop-unofficial-mirror/xorg__driver__xf86-video-armsoc,OtherCrashOverride/armsoc-hardkernel,commshare/xf86-video-armsoc,Popolon/xf86-video-armsoc,xin3liang/xf86-video-armsoc,Popolon/xf86-video-armsoc,apxii/xf86-video-armsoc,singulared/xf86-video-armsoc,singulared/xf86-video-armsoc