msm: mdss: fix the vsync event notification on 8x10

When client is turning off the vsync event notification,
use complete instead of complete_all, which will cause
unwanted user thread wake-up.

Change-Id: I70f7c6b877cb0df7ccd980437c7d12a6148bbe77
Signed-off-by: Xiaoming Zhou <zhoux@codeaurora.org>