rust: devres: fix private intra-doc link

rust: devres: fix private intra-doc link

The future move of pin-init to `syn` uncovers the following private
intra-doc link:

    error: public documentation for `Devres` links to private item `Self::inner`
       --> rust/kernel/devres.rs:106:7
        |
    106 | /// [`Self::inner`] is guaranteed to be initialized and is always accessed read-only.
        |       ^^^^^^^^^^^ this item is private
        |
        = note: this link will resolve properly if you pass `--document-private-items`
        = note: `-D rustdoc::private-intra-doc-links` implied by `-D warnings`
        = help: to override `-D warnings` add `#[allow(rustdoc::private_intra_doc_links)]`

Currently, when rendered, the link points to "nowhere" (an inexistent
anchor for a "method").

Thus fix it.

Cc: stable@vger.kernel.org
Fixes: f5d3ef25d238 ("rust: devres: get rid of Devres' inner Arc")
Acked-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patch.msgid.link/20251029071406.324511-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>