rust: kernel: list: fix incorrect pop_back example comment

The example uses pop_back(), but the accompanying comment says
pop_front(). Update the comment to match the example.

Signed-off-by: Nikolai Grlica <nikolai@nikolaigrlica.dev>
Cc: stable@vger.kernel.org
Fixes: bf87a41b85 ("rust: list: Add an example for `ListLinksSelfPtr` usage")
Link: https://patch.msgid.link/20260810150322.61809-1-nikolai@nikolaigrlica.dev
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

rust/kernel/list.rs

@@ -249,7 +249,7 @@ pub use self::arc_field::{
 ///     assert_eq!(list.iter().count(), 3);
 /// }
 ///
-/// // Pop the items from the list using `pop_front()` and verify the content.
+/// // Pop the items from the list using `pop_back()` and verify the content.
 /// {
 ///     assert_eq!(list.pop_back().ok_or(EINVAL)?.value.foo(), ("a", 15));
 ///     assert_eq!(list.pop_back().ok_or(EINVAL)?.value.foo(), ("a", 32));