selftests/bpf: Fix spelling mistake.

There is a spelling mistake in an ASSERT_OK literal string. Fix it.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Acked-by: Mykola Lysenko <mykolal@fb.com>
Link: https://lore.kernel.org/r/20220817213242.101277-1-colin.i.king@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>