disp: msm: dsi: signal pending clock change in case of DMS

When there is a change in resolution or FPS, a new clock rate is
calculated. During such a Dynamic Mode Switch, the clock rate
change pending flag needs to be set after it has been calculated.
This flag is later checked before kickoff and the clocks are updated
accordingly.

Change-Id: Iec102796d5c61d01c567f0b6676e9a6d4ed94268
Signed-off-by: Satya Rama Aditya Pinapala <psraditya30@codeaurora.org>