drm/dp_mst: Separate @failing_port list in drm_dp_mst_atomic_check_mgr() comment

drm/dp_mst: Separate @failing_port list in drm_dp_mst_atomic_check_mgr() comment

Stephen Rothwell reported htmldocs warnings when merging drm-intel
tree:

Documentation/gpu/drm-kms-helpers:296: drivers/gpu/drm/display/drm_dp_mst_topology.c:5484: ERROR: Unexpected indentation.
Documentation/gpu/drm-kms-helpers:296: drivers/gpu/drm/display/drm_dp_mst_topology.c:5488: WARNING: Block quote ends without a blank line; unexpected unindent.

Separate @failing_port return value list by surrounding it with a
blank line to fix above warnings.

Fixes: 1cd0a5ea427931 ("drm/dp_mst: Factor out a helper to check the atomic state of a topology manager")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Closes: https://lore.kernel.org/linux-next/20231114141715.6f435118@canb.auug.org.au/
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231114081033.27343-1-bagasdotme@gmail.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>