Fix struct uniform packing. Our current code would not adapt properly for members that did not fit in the previous register. Instead, use the correct adjusted value as returned from the block layout encoder. This fixes a dEQP WebGL test: gles2/shaders/linkage. BUG=angle:910 Change-Id: Id77d0c76ce767665b3db97cb4d14e8008254fd9f Reviewed-on: https://chromium-review.googlesource.com/247241 Tested-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Zhenyao Mo <zmo@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>