drm/msm: fix watchdog vsync source for dsi display

Commit 483d9364 ("drm/msm: update sde rsc support
with wd vsync") updated watchdog vsync source based
on recommended register programming. The register
programming recommendation is changed and this patch
fixes the vsync source based on new recommended
values.

Change-Id: I99abc09f1ef0ff5b39759b45a06245343f8d1aaa
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>