blk-mq: ABI/sysfs-block: fix docs build warnings

blk-mq: ABI/sysfs-block: fix docs build warnings

Clean up the async_depth documentation:
- insert blank lines before and after lists where needed
- convert verb tense in a few places
- make lines fit within 80 characters

Documentation/ABI/stable/sysfs-block:612: ERROR: Unexpected indentation. [docutils]
Documentation/ABI/stable/sysfs-block:612: ERROR: Unexpected indentation. [docutils]
Documentation/ABI/stable/sysfs-block:612: ERROR: Unexpected indentation. [docutils]

Fixes: 2c04718edcd5 ("blk-mq: add documentation for new queue attribute async_dpeth")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>