drm/dp_mst: Use drm_dp_dpcd_write_data() to write GUID for non-root MST branch devices

drm/dp_mst: Use drm_dp_dpcd_write_data() to write GUID for non-root MST branch devices

drm_dp_dpcd_write_data() can be used to write the GUID for a non-root
MST branch device, similarly to writing the GUID to a root MST branch
device, do so.

Cc: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc: Lyude Paul <lyude@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://lore.kernel.org/r/20250401103846.686408-2-imre.deak@intel.com