Use DIV_ROUND_UP to prevent truncation by integer division issue.
This ensures we return enough delay time.

Also fix returning negative value when new_sel < old_sel.
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Link: https://lore.kernel.org/r/20210618141412.4014912-1-axel.lin@ingics.comSigned-off-by: Mark Brown <broonie@kernel.org>