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

There are a couple of spelling mistakes, one in a literal string and one
in a comment. Fix them.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20220928221555.67873-1-colin.i.king@gmail.com