drm/tve200: fix kernel-doc documentation comment include

The DOC: line acts as an identifier for the :doc: include. Fixes:

./drivers/gpu/drm/tve200/tve200_drv.c:1: warning: no structured comments found

Cc: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180220142008.9330-1-jani.nikula@intel.com