sed-opal: add helper to get multiple columns at once.

Refactors current code querying single column to use the
new helper. Real multi column usage will be added later.

Signed-off-by: Ondrej Kozina <okozina@redhat.com>
Tested-by: Luca Boccassi <bluca@debian.org>
Tested-by: Milan Broz <gmazyland@gmail.com>
Acked-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230405111223.272816-5-okozina@redhat.com


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