crypto: chacha20-ssse3 - Align stack pointer to 64 bytes

This aligns the stack pointer in chacha20_4block_xor_ssse3 to 64 bytes.
Fixes general protection faults and potential kernel panics.

Cc: stable@vger.kernel.org
Signed-off-by: Eli Cooper <elicooper@gmx.com>
Acked-by: Martin Willi <martin@strongswan.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>