drm/msm/dp: call dp_display_get_next_bridge() during probe

The funcion dp_display_get_next_bridge() can return -EPROBE_DEFER if the
next bridge is not (yet) available. However returning -EPROBE_DEFER from
msm_dp_modeset_init() is not ideal. This leads to -EPROBE return from
component_bind, which can easily result in -EPROBE_DEFR loops.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>