block: remove a duplicate definition for bdev_read_only

bdev_read_only is already defined as an inline function in blkdev.h.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20241119160932.1327864-6-hch@lst.de


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