msm: dsi: Do not divide porch parameters when FBC is enabled

Horizontal porch values for DSI were set incorrectly when
Frame-Buffer Compression(FBC) is enabled. This fixes incorrect
DSI clock frequency calculations when FBC is enabled.

Change-Id: Iba9c3fc193148e3dcb31f1c11a37ae120e8707d1
Signed-off-by: Siddhartha Agrawal <agrawals@codeaurora.org>