drm/client: fix kernel-doc warning in drm_client.h

drm/client: fix kernel-doc warning in drm_client.h

scripts/kernel-doc complains about the comment for hotplug_failed,
so fix it:

include/drm/drm_client.h:111: warning: Incorrect use of kernel-doc format:          * @hotplug failed:

Fixes: 6a9d5ad3af65 ("drm/client: Add hotplug_failed flag")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230131012107.20943-1-rdunlap@infradead.org