ttusb2: Don't use stack variables for DMA

ttusb2: Don't use stack variables for DMA

commit ff17999184ed13829bc14c3be412d980173dff40 upstream.

The ttusb2_msg function uses on-stack variables to submit commands to
dvb_usb_generic.  This eventually gets to the DMA api layer and will throw a
traceback if the debugging options are set.

This allocates the temporary buffer variables with kzalloc instead.

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=734506

Signed-off-by: Josh Boyer <jwboyer@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>