[media] lmedm04: get rid of on-stack dma buffers

usb_control_msg initiates (and waits for completion of) a dma transfer using
the supplied buffer. That buffer thus has to be seperately allocated on
the heap.

In lib/dma_debug.c the function check_for_stack even warns about it:
	WARNING: at lib/dma-debug.c:866 check_for_stack

Tested-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Florian Mickler <florian@mickler.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>