drm/i915: turn some bogus kernel-doc comments to normal comments

Apparently accidental or misplaced /** kernel-doc comments, confusing
the tool. Turn them to normal comments.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1453101588-18008-2-git-send-email-jani.nikula@intel.com