block: Use bio_sectors() more consistently

block: Use bio_sectors() more consistently

Bunch of places in the code weren't using it where they could be -
this'll reduce the size of the patch that puts bi_sector/bi_size/bi_idx
into a struct bvec_iter.

Signed-off-by: Kent Overstreet <[email protected]>
CC: Jens Axboe <[email protected]>
CC: "Ed L. Cashin" <[email protected]>
CC: Nick Piggin <[email protected]>
CC: Jiri Kosina <[email protected]>
CC: Jim Paris <[email protected]>
CC: Geoff Levand <[email protected]>
CC: Alasdair Kergon <[email protected]>
CC: [email protected]
CC: Neil Brown <[email protected]>
CC: Steven Rostedt <[email protected]>
Acked-by: Ed Cashin <[email protected]>