interactive: Fix PSK ring buffer bug

I introduced a regression in af4866f49b4 (interactive: Make libraries
buildable) by putting bpsk_varicode into progmem without updating the
accessors.

As progmem access is broken on uin16_t arrays with the Arduino 1.0
toolchain, we will not put the varicode buffer in progmem.

Signed-off-by: Joel Stanley <joel@jms.id.au>