drm/msm/dsi: Fix an error code in msm_dsi_modeset_init()

Return an error code if msm_dsi_manager_validate_current_config().
Don't return success.

Fixes: 8b03ad30

 ("drm/msm/dsi: Use one connector for dual DSI mode")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20211001123308.GF2283@kili
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>