block: remove the NULL ioc check in put_io_context

No caller passes in a NULL pointer, so remove the check.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20211209063131.18537-5-hch@lst.de


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