V4L/DVB: media/az6027: doing dma on the stack

I changed the dma buffers to use allocated memory instead of stack
memory.

The reason for this is documented in Documentation/DMA-API-HOWTO.txt
under the section:  "What memory is DMA'able?"  That document was only
added a couple weeks ago and there are still lots of modules which
haven't been corrected yet.  Btw. Smatch includes a pretty good test to
find places which use stack memory as a dma buffer.  That's how I found
these.  (http://smatch.sf.net).

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>