Fix incorrect error check. 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/218507 Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>