ANDROID: rust_binder: fix leak of name in binderfs

The `rust_binder_new_device` method just makes a copy of the provided c
string, and does not take ownership of it. This means that there's no
reason to kmemdup the string. Also, outside of the error path, the name
is not freed.

Fixes: 0d512d37 ("ANDROID: rust_binder: add binderfs support to Rust binder")
Change-Id: I4cb63ff0c46d04da7f9debfa9896113779856c02
Signed-off-by: Alice Ryhl <aliceryhl@google.com>