drm/connector: Fix kerneldoc warning in HDR_OUTPUT_METADATA description

Fixes the following warning:
../drivers/gpu/drm/drm_connector.c:981: WARNING: Definition list ends without a blank line; unexpected unindent.

Fixes: a09db883 ("drm: Fix docbook warnings in hdr metadata helper structures")
Cc: Shashank Sharma <shashank.sharma@intel.com>
Cc: Ville Syrjä <ville.syrjala@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: Sean Paul <sean@poorly.run>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: "Ville Syrjä" <ville.syrjala@linux.intel.com>
Cc: Hans Verkuil <hansverk@cisco.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-fbdev@vger.kernel.org
Cc: Sean Paul <sean@poorly.run> (v1)
Cc: Uma Shankar <uma.shankar@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190613151727.133696-1-sean@poorly.run