[PATCH] rust: device: allow `dead_code` for `Device<>::parent()`

[Miguel Ojeda <ojeda@kernel.org>]

When `CONFIG_AUXILIARY_BUS` is disabled, `parent()` is still dead code:

    error: method `parent` is never used
      --> rust/kernel/device.rs:71:19
       |
    64 | impl<Ctx: DeviceContext> Device<Ctx> {
       | ------------------------------------ method in this implementation
    ...
    71 |     pub(crate) fn parent(&self) -> Option<&Self> {
       |                   ^^^^^^
       |
       = note: `-D dead-code` implied by `-D warnings`
       = help: to override `-D warnings` add `#[allow(dead_code)]`

Thus reintroduce the `expect`, but now as an `allow`, and do so as
`dead_code` since that is narrower.

Fixes: ce735e73dd59 ("rust: auxiliary: add auxiliary device / driver abstractions")
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
I should have noticed this earlier, sorry. Please feel free to rebase to
fix it directly there if you prefer.

 rust/kernel/device.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
index 40c1f549b0ba..e8ab4b9617db 100644
--- a/rust/kernel/device.rs
+++ b/rust/kernel/device.rs
@@ -68,6 +68,7 @@ pub(crate) fn as_raw(&self) -> *mut bindings::device {
     }

     /// Returns a reference to the parent device, if any.
+    #[allow(dead_code)]
     pub(crate) fn parent(&self) -> Option<&Self> {
         // SAFETY:
         // - By the type invariant `self.as_raw()` is always valid.

base-commit: ce735e73dd59b169b877cedd0753297c81c2a091
--
2.49.0