[media] tm6000: Plug memory leak on PCM free

When releasing hardware resources, the DMA buffer allocated to the PCM
device needs to be freed to prevent a memory leak.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>