This fixes some broken tests in dEQP:
functional.shaders.conversions.scalar_to_matrix

BUG=angle:712

Change-Id: Ia01d720307ea6ca70da266b2085a878eaaab2412
Reviewed-on: https://chromium-review.googlesource.com/210881Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Nicolas Capens <capn@chromium.org>