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: 6a9d5ad ("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

Author: rddunlap

include/drm/drm_client.h

@@ -108,7 +108,7 @@ struct drm_client_dev {
 	struct drm_mode_set *modesets;
 
 	/**
-	 * @hotplug failed:
+	 * @hotplug_failed:
 	 *
 	 * Set by client hotplug helpers if the hotplugging failed
 	 * before. It is usually not tried again.