block: use blk_rq_map_user_iov to implement blk_rq_map_user

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --cc block/bio.c
Simple merge

diff --cc block/blk-map.c
Simple merge

diff --cc include/linux/bio.h
Simple merge