drm/msm/dsi: Convert to clk_hw based provider APIs

We're removing struct clk from the clk provider API, so switch
this code to using the clk_hw based provider APIs.

Cc: Wentao Xu <wentaox@codeaurora.org>
Cc: Rob Clark <robdclark@gmail.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>