drm/msm/hdmi: convert to msm_clk_get()

We already have, as a result of upstreaming the gpu bindings,
msm_clk_get() which will try to get the clock both without and with a
"_clk" suffix.  Use this in HDMI code so we can drop the "_clk" suffix
in bindings while maintaing backwards compatibility.

Signed-off-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>