Don't decrement bi_size in bio_endio

The only caller of bio_endio that does not pass the full bi_size
is end_that_request_first.  Also, no ->bi_end_io method is really
interested in bi_size being decremented.

So move the decrement and related code into ll_rw_blk and merge it
with order_bio_endio to form req_bio_endio which does endio functionality
specific to request completion.

As some ->bi_end_io methods do check bi_size of 0, we set it thus for
now, but that will go in the next patch.

Signed-off-by: Neil Brown <neilb@suse.de>

### Diffstat output
 ./block/ll_rw_blk.c |   42 +++++++++++++++++++++++++++---------------
 ./fs/bio.c          |   23 +++++++++++------------
 2 files changed, 38 insertions(+), 27 deletions(-)

diff .prev/block/ll_rw_blk.c ./block/ll_rw_blk.c
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>