Fix aligned access regression.

This fixes commit cd0ea23407fb36528388cd6705f0150c0972963e.

Change-Id: I51c82049fa809f303401b6623dbaa947a50d6d62
Reviewed-on: https://swiftshader-review.googlesource.com/4519
Tested-by: Nicolas Capens <capn@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>