drm: todo: Avoid accidental crossreferences

RST uses underscores at the end of words to create crossreferences and
it will accidentally try to link to tinydrm_ and drm_fb_ targets from
the TODO, which is clearly not the intention in this context.

Use backslashes to escape the special meaning of the underscore.
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170731124259.7495-1-thierry.reding@gmail.com

Documentation/gpu/todo.rst

@@ -108,8 +108,8 @@ This would be especially useful for tinydrm:
   crtc state, clear that to the max values, x/y = 0 and w/h = MAX_INT, in
   __drm_atomic_helper_crtc_duplicate_state().
 
-- Move tinydrm_merge_clips into drm_framebuffer.c, dropping the tinydrm_
-  prefix ofc and using drm_fb_. drm_framebuffer.c makes sense since this
+- Move tinydrm_merge_clips into drm_framebuffer.c, dropping the tinydrm\_
+  prefix ofc and using drm_fb\_. drm_framebuffer.c makes sense since this
   is a function useful to implement the fb->dirty function.
 
 - Create a new drm_fb_dirty function which does essentially what e.g.