drm/msm/dsi: set default num_data_lanes

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>