disp: msm: sde: initialize list head of irq node

List head should be initialized after the irq node is allocated.
Change initializes the list head of the node.

Change-Id: I495751fcf2422bba3f39a0719e2d76738b691dd9
Signed-off-by: Lakshmi Narayana Kalavala <lkalaval@codeaurora.org>