drm/msm/dsi: set default num_data_lanes

If "data_lanes" property of the dsi output endpoint is missing in
the DT, num_data_lanes would be 0 by default, which could cause
dsi_host_attach() to fail if dsi->lanes is set to a non-zero value
by the bridge driver.

According to the binding document of msm dsi controller, the
input/output endpoint of the controller is expected to have 4 lanes.
So let's set num_data_lanes to 4 by default.

Signed-off-by: Philip Chen <philipchen@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20211030100812.1.I6cd9af36b723fed277d34539d3b2ba4ca233ad2d@changeid
Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/dsi/dsi_host.c

@@ -1658,6 +1658,8 @@ static int dsi_host_parse_lane_data(struct msm_dsi_host *msm_host,
 	if (!prop) {
 		DRM_DEV_DEBUG(dev,
 			"failed to find data lane mapping, using default\n");
+		/* Set the number of date lanes to 4 by default. */
+		msm_host->num_data_lanes = 4;
 		return 0;
 	}