rust: list: fix path of assert_pinned!

Commit dbd5058 ("rust: make pin-init its own crate") moved all
items from pin-init into the pin-init crate, including the
`assert_pinned!` macro.

Thus fix the path of the sole user of the `assert_pinned!` macro.

This occurrence was missed in the commit above, since it is in a macro
rule that has no current users (although binder is a future user).

Cc: stable@kernel.org
Fixes: dbd5058 ("rust: make pin-init its own crate")
Signed-off-by: Benno Lossin <lossin@kernel.org>
Link: https://lore.kernel.org/r/20250525173450.853413-1-lossin@kernel.org
[ Reworded slightly as discussed in the list. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: BennoLossin

rust/kernel/list/arc.rs

@@ -96,7 +96,7 @@ macro_rules! impl_list_arc_safe {
     } $($rest:tt)*) => {
         impl$(<$($generics)*>)? $crate::list::ListArcSafe<$num> for $t {
             unsafe fn on_create_list_arc_from_unique(self: ::core::pin::Pin<&mut Self>) {
-                $crate::assert_pinned!($t, $field, $fty, inline);
+                ::pin_init::assert_pinned!($t, $field, $fty, inline);
 
                 // SAFETY: This field is structurally pinned as per the above assertion.
                 let field = unsafe {