mdss: dsi: fix DSI clk rate update during dynamic resolution switch

Current implementation updates the DSI link clock rate during UNBLANK.
By this time link rate is already set with a random value, which
might lead to unexpected behaviour. Update the clock during LINK READY
so that the new  values take effect.

Change-Id: Ib6d3f27b5607adb1d47ec5b8094af4f280424c2b
Signed-off-by: Anusha Koduru <kanusha@codeaurora.org>