msm: clock-8960: Change source of DSI escape clock to byte clock

Changing DSI escape clock source from PXO to byte clock to add
flexibilty for customers. They can modify the escape clock by
changing the pinfo divider.

Change-Id: I3ad072fc524fe5fae9695a55bba24ce23b97efc7
CRs-Fixed: 361022
Signed-off-by: Siddhartha Agrawal <agrawals@codeaurora.org>