block: remove elevator queue's type check in elv_attr_show/store()

block: remove elevator queue's type check in elv_attr_show/store()

elevatore queue's type is assigned since its allocation, and never
get cleared until it is released.

So its ->type is always not NULL, remove the unnecessary check.

Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250505141805.2751237-19-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>