selftests/bpf: Update error message in negative linked_list test

Some error messages are changed due to the addition of
percpu kptr support. Fix linked_list test with changed
error messages.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20230827152754.1997769-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>