msm: mdss: do not update polarity for DSI interface

Polarity should be updated based on HDMI resolution
for HDMI display. However, DSI interface does not need
to update polarity.

CRs-Fixed: 2046790
Change-Id: I4a30fcd7ebec70224accd2178c14bd37d2059f4e
Signed-off-by: zhaoyuan <yzhao@codeaurora.org>