block: refactor put_iocontext_active

Factor out a ioc_exit_icqs helper to tear down the icqs and the fold
the rest of put_iocontext_active into exit_io_context.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20211209063131.18537-4-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>