disp: msm: dsi: recount drm mode count

Drm driver will remove the same mode that defined
in dsi panel dtsi. But the mode count was not updated,
so when checked drm mode, need to recount the mode.

Change-Id: I51a2c40ceb7d4ee83a15f74d9d724b4fb9c8a618
Signed-off-by: Zhao, Yuan <yzhao@codeaurora.org>