This fixes a use-after-free bug in the handling of split transactions.
The AT DMA handler of the request was occasionally executed after the
AR DMA handler of the response.  The AT DMA handler then accessed an
already freed packet.

Reported by Johannes Berg.
http://bugzilla.kernel.org/show_bug.cgi?id=9617Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Tested-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Jarod Wilson <jwilson@redhat.com>