rust: arc: move From<UniqueArc<T>> for Pin<UniqueArc<T>> impl

This is part of the effort to minimize the differences of the `rust`
branch with respect to mainline in order to eventually drop it.

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

rust/kernel/sync/arc.rs

@@ -370,14 +370,6 @@ impl<T: ?Sized> From<UniqueArc<T>> for Arc<T> {
     }
 }
 
-impl<T: ?Sized> From<UniqueArc<T>> for Pin<UniqueArc<T>> {
-    fn from(obj: UniqueArc<T>) -> Self {
-        // SAFETY: It is not possible to move/replace `T` inside a `Pin<UniqueArc<T>>` (unless `T`
-        // is `Unpin`), so it is ok to convert it to `Pin<UniqueArc<T>>`.
-        unsafe { Pin::new_unchecked(obj) }
-    }
-}
-
 impl<T: ?Sized> From<Pin<UniqueArc<T>>> for Arc<T> {
     fn from(item: Pin<UniqueArc<T>>) -> Self {
         // SAFETY: The type invariants of `Arc` guarantee that the data is pinned.
@@ -551,6 +543,14 @@ impl<T> UniqueArc<MaybeUninit<T>> {
     }
 }
 
+impl<T: ?Sized> From<UniqueArc<T>> for Pin<UniqueArc<T>> {
+    fn from(obj: UniqueArc<T>) -> Self {
+        // SAFETY: It is not possible to move/replace `T` inside a `Pin<UniqueArc<T>>` (unless `T`
+        // is `Unpin`), so it is ok to convert it to `Pin<UniqueArc<T>>`.
+        unsafe { Pin::new_unchecked(obj) }
+    }
+}
+
 impl<T: ?Sized> Deref for UniqueArc<T> {
     type Target = T;