ASoC: kirkwood: prevent double streaming

The kirkwood audio subsystem presents 2 PCM's for one source.
Streaming on a second PCM while the first one is active
cuts this last one.
Then, ending the last stream gives a kernel trap in free_irq().

Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mark Brown <broonie@kernel.org>