drm: Fix up markup fumble

It's & for struct references, not #.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Acked-by: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1462369327-26659-1-git-send-email-daniel.vetter@ffwll.ch