disp: msm: dsi: update dsi pclk in panel mode settings

Change calculates and updates correct pclk that is being
used to drm modes in kilo hertz.

Change-Id: I7aab10c08689697120d4d7c152f30993defd36d3
Signed-off-by: Vara Reddy <varar@codeaurora.org>
Signed-off-by: Ray Zhang <rayz@codeaurora.org>
Signed-off-by: Bruce Hoo <bingchua@codeaurora.org>