drm/dsi: fix dsi control power supply turn off sequence

Current implementation leaves dsi control power supply in
ON mode when drm calls bridge disable API. This patch
fixes the sequence to avoid control power rail leakage.

Change-Id: I6d8b6438e9b67f474f7a45ae947219a878c9f6c0
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>