The registers variable became a pointer but this error check was not
updated.

BUG=angle:743

Change-Id: Id2cd7b5ba39180281a3bbc408cd7c31bc663500c
Reviewed-on: https://chromium-review.googlesource.com/218507Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>