msm: trout: change name of pmdh_clk to mddi_clk

This clock is used in the framebuffer driver as mddi_clk.
This just changes the name to match that. This also
mirrors a change in Google tree.

Signed-off-by: Daniel Walker <dwalker@codeaurora.org>
Signed-off-by: David Brown <davidb@codeaurora.org>