drm/msm/dsi: bypass dsi clock set during changing mode

Bypass setting clkrate_change_pending flag if the current mode
and the mode to be set has the same preferred clock rate.

Change-Id: Id1f6c45e822492427cf3555beeaa5f0e7ea3243c
Signed-off-by: Vara Reddy <varar@codeaurora.org>