msm: clock-mdss-8974: Enable the MDSS AHB clock for HDMI PLL programming

Accesses to the HDMI PLL registers require the MDSS AHB clock
to be on. Ensure that this clock is on before touching those
registers.

Change-Id: I77647b62a8ee9da9ae6813a185fca64256108f65
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>