While this function on its own passes all of fate-hevc, there's
indications that the function might need to handle widths that
aren't a multiple of 8 (noted in commit
f63f9be37c799ddc835af358034630d31fb7db02, which later was
reverted).
Signed-off-by: Martin Storsjö <martin@martin.st>
(cherry picked from commit 24b93022fee322c7a17e326e2d162a1fbc3698ee)
6ff38630e1