drm/connector: use drm_sysfs_connector_hotplug_event

In drm_connector_register, use drm_sysfs_connector_hotplug_event
instead of drm_sysfs_hotplug_event, because the hotplug event
only updates a single connector.

Signed-off-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211018084707.32253-4-contact@emersion.fr