disp: msm: sde: remove an uninitialized index variable

Avoid exposing any uninitialized data when setting up the
interrupt tables.

Change-Id: I00d3dc8b5acc843401148585a129fde58e326beb
Signed-off-by: Narendra Muppalla <NarendraM@codeaurora.org>
Signed-off-by: Steve Cohen <cohens@codeaurora.org>