ASoC: au1x: dbdma2: plug memleak in pcm device creation error path

free the allocated pcm platform device in the error path.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>