[PATCH] Fix block layer bug handling of partial bvec completion

[PATCH] Fix block layer bug handling of partial bvec completion

Noted by Sean Estabrooks:

There is a bug in "ll_rw_blk.c" handling partial bvec submissions.
For whatever reason the floppy driver was triggering it more than
other users (most likely because most other devices tend to be able
to always complete a full request in one go).

Fixed by updating the proper bio vector index entry.