blk-mq: Fix more tag iteration function documentation

blk-mq: Fix more tag iteration function documentation

Commit 8ab30a331946 ("blk-mq: Drop busy_iter_fn blk_mq_hw_ctx argument")
removed the hctx argument from the callback functions called by
bt_for_each() and blk_mq_queue_tag_busy_iter(). Commit 2dd6532e9591
("blk-mq: Drop 'reserved' arg of busy_tag_iter_fn") removed the
'reserved' argument of the busy_tag_iter_fn function pointer type. Bring
the documentation of the tag iteration functions in sync with these
changes.

Cc: John Garry <john.g.garry@oracle.com>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>