drm/msm/dsi: Use msm_clk_get in dsi_get_config

We try to get the interface clock in dsi_get_config early during DSI's
component bind. Try getting both the "iface" and "iface_clk" clock name
variants so that we are compatible with both new and legacy DT.

Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>