block: add helper for checking if queue is registered

There are 4 users which check if queue is registered, so add one helper
to check it.

Cc: Christoph Hellwig <[email protected]>
Cc: Hannes Reinecke <[email protected]>
Cc: Greg KH <[email protected]>
Cc: Mike Snitzer <[email protected]>
Cc: Bart Van Assche <[email protected]>
Reviewed-by: Bart Van Assche <[email protected]>
Signed-off-by: Ming Lei <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

0 files changed, 0 insertions, 0 deletions