[media] DiB0700: get rid of on-stack dma buffers

This patch removes the on-stack buffers for USB DMA transfers.

This is an alternative version of the patch discussed by Florian here:
http://thread.gmane.org/gmane.linux.kernel/1115695/



Signed-off-by: Olivier Grenie <olivier.grenie@dibcom.fr>
Signed-off-by: Patrick Boettcher <patrick.boettcher@dibcom.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>