A refactoring bug slipped in that used the non-transposed row count
for non-square matrices, causing an ASSERT failure in Debug. It's
unfortunately not easy to revert the previous change, so instead
fix it here.

BUG=angleproject:1129

Change-Id: I0de66de46a24b402c93da68f189a2c65616c2006
Reviewed-on: https://chromium-review.googlesource.com/294641Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>