This was an oversight from the previous CL. It doesn't really matter
with the current code generation pattern, since the upper bits of the
index will always be zero, but that might change in the future.

Bug: chromium:225811
Change-Id: I568a0824cad9ce9b73a56decc15d146c7dc675a1
Reviewed-on: https://chromium-review.googlesource.com/1174111
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55104}