[arm64]: Fix bug introduced accidentally in r30710

[arm64]: Fix bug introduced accidentally in r30710

Uncomment the if (!serializer_enabled()) check which I accidentially left
commented out after debugging during the CLs development.

BUG=chromium:532969
R=bmeurer@chromium.org
LOG=n

Committed: https://crrev.com/2088752c709f3f921685e6bc27b2fe7fd22f2aac
Cr-Commit-Position: refs/heads/master@{#30811}

[rmcilroy, 2015-09-17 15:48:09]

rmcilroy@chromium.org changed reviewers:
+ bmeurer@chromium.org

[rmcilroy, 2015-09-17 15:48:09]

Benedikt, could you take a quick look please? Oops....

[rmcilroy, 2015-09-17 15:59:52]

rmcilroy@chromium.org changed reviewers:
+ mstarzinger@chromium.org
- bmeurer@chromium.org

[rmcilroy, 2015-09-17 15:59:52]

Michi: could you take a look please since Benedikt's already left?

[rmcilroy, 2015-09-17 16:44:01]

TBRing.

[rmcilroy, 2015-09-17 16:44:04]

The CQ bit was checked by rmcilroy@chromium.org

[commit-bot: I haz the power, 2015-09-17 16:44:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1351943002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1351943002/1

[Benedikt Meurer, 2015-09-17 16:49:56]

bmeurer@chromium.org changed reviewers:
+ bmeurer@chromium.org

[Benedikt Meurer, 2015-09-17 16:49:56]

LGTM

[commit-bot: I haz the power, 2015-09-17 17:05:06]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-17 17:05:06]

Try jobs failed on following builders:
  v8_presubmit on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_presubmit/builds/5897)

[Benedikt Meurer, 2015-09-17 17:16:42]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-09-17 17:16:56]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1351943002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1351943002/1

[commit-bot: I haz the power, 2015-09-17 17:24:17]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-17 17:24:29]

Patchset 1 (id:??) landed as
https://crrev.com/2088752c709f3f921685e6bc27b2fe7fd22f2aac
Cr-Commit-Position: refs/heads/master@{#30811}