drm/todo: mention i915 in the struct_mutex section

The i915 driver uses the struct_mutex, eventhough it does not use the
locked version of the drm_object_gem API.

Signed-off-by: Emil Velikov <[e-mail]>
Acked-by: Sam Ravnborg <[e-mail]>
Reviewed-by: Daniel Vetter <[e-mail]>
Acked-by: Thomas Zimmermann <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

Documentation/gpu/todo.rst

···
 reliably take that lock any more. Instead state needs to be protected with
 suitable subordinate locks or some cleanup work pushed to a worker thread. For
 performance-critical drivers it might also be better to go with a more
-fine-grained per-buffer object and per-context lockings scheme. Currently only the
-``msm`` driver still use ``struct_mutex``.
+fine-grained per-buffer object and per-context lockings scheme. Currently only
+the ``msm`` and `i915` drivers use ``struct_mutex``.
 
 Contact: Daniel Vetter, respective driver maintainers