selftests/bpf: Fix spelling mistake: "unpriviliged" -> "unprivileged"

There are spelling mistakes in ASSERT messages. Fix these.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220523115604.49942-1-colin.i.king@gmail.com