Only call bi_end_io once for any bio

Currently bi_end_io can be called multiple times as sub-requests
complete.  However no ->bi_end_io function wants to know about that.
So only call when the bio is complete.

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

### Diffstat output
 ./fs/bio.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

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