altos: Increase AES IV buffer to hold maximum AES state

altos: Increase AES IV buffer to hold maximum AES state

The compiler emits warnings if this buffer is only 16 bytes. I'm hoping
that's because the max key size could be 256 bits instead of 128 bits?

In any case, this makes the compiler happy.

Signed-off-by: Keith Packard <keithp@keithp.com>