ANDROID: rust_binder: access lru list through private data

When changing Rust Binder to use the new alloc_shrinker(), the layout
was changed so that lru_list is no longer stored next to the shrinker
object, but some shrinker callbacks were not updated to reflect that.
Thus, access the lru list through the shrinker's private data pointer,
instead of using a container_of operation.

Bug: 424727800
Change-Id: Iac09b2d81e555c3554101231de701dfa79b0e644
Signed-off-by: Alice Ryhl <aliceryhl@google.com>