drm: Clean up planes in atomic commit helper failure path

If waiting for fences fails for blocking commits, planes must be cleaned
up before returning.

Cc: stable@vger.kernel.org
Fixes: f6ce410a ("drm/fence: allow fence waiting to be interrupted by userspace")
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170102231427.7192-1-laurent.pinchart@ideasonboard.com