zbd: don't lock zones outside working area

zbd: don't lock zones outside working area

Currently threads lock each other zones even if their working areas as
defined by [f->file_offset, f->file_offset + f->io_size) don't intersect.
This leads to unnecessary quiescing.

Patch clamps every zone to [->min_zone, ->max_zone) when doing search
for opened zone and more importantly adds an assert so that any
unnecessary zone locking becomes very visible.

Signed-off-by: Alexey Dobriyan (SK hynix) <adobriyan@gmail.com>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>