wireguard: kconfig: use arm chacha even with no neon

The condition here was incorrect: a non-neon fallback implementation is
available on arm32 when NEON is not supported.

Reported-by: Ilya Lipnitskiy <ilya.lipnitskiy@gmail.com>
Fixes: e7096c13

 ("net: WireGuard secure network tunnel")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>