Take advantage of the fact that if the auxiliary device is bound the
parent is guaranteed to be bound as well and implement a separate
parent() method for auxiliary::Device<Bound>.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/auxiliary.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/rust/kernel/auxiliary.rs b/rust/kernel/auxiliary.rs
index 497601f7473b..cc67fa5ddde3 100644
--- a/rust/kernel/auxiliary.rs
+++ b/rust/kernel/auxiliary.rs
@@ -217,6 +217,16 @@ pub fn id(&self) -> u32 {
     }
 }
 
+impl Device<device::Bound> {
+    /// Returns a bound reference to the parent [`device::Device`].
+    pub fn parent(&self) -> &device::Device<device::Bound> {
+        let parent = (**self).parent();
+
+        // SAFETY: A bound auxiliary device always has a bound parent device.
+        unsafe { parent.as_bound() }
+    }
+}
+
 impl Device {
     /// Returns a reference to the parent [`device::Device`].
     pub fn parent(&self) -> &device::Device {
-- 
2.51.0