This patch fixes bio leaks in SG_IO. rq->bio can be changed after io
completion, so we need to reset rq->bio before calling blk_rq_unmap_user()

http://marc.theaimsgroup.com/?l=linux-kernel&m=116570666807983&w=2Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>