msm_fb: display: remove wait4vsync during dtv off

After timing generator is disabled, vsync interrupt may not come,
which causes wait4vsync hang and device crashes when the hdmi cable is
unplugged.

Signed-off-by: Huaibin Yang <huaibiny@codeaurora.org>
Signed-off-by: Naseer Ahmed <naseer@codeaurora.org>

Change-Id: I80ca2fc8f0c75ab818eff083b47f4040504668fc