block: renumber and rename the cache disabled flag

Start with the first bit, and drop the plural-S from the name.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20240619154623.450048-4-hch@lst.de


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