dm: use bdev_read_only to check if a device is read-only

dm-thin and dm-cache also work on partitions, so use the proper
interface to check if the device is read-only.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/dm-cache-metadata.c

@@ -449,7 +449,7 @@ static int __check_incompat_features(struct cache_disk_superblock *disk_super,
 	/*
 	 * Check for read-only metadata to skip the following RDWR checks.
 	 */
-	if (get_disk_ro(cmd->bdev->bd_disk))
+	if (bdev_read_only(cmd->bdev))
 		return 0;
 
 	features = le32_to_cpu(disk_super->compat_ro_flags) & ~DM_CACHE_FEATURE_COMPAT_RO_SUPP;

drivers/md/dm-thin-metadata.c

@@ -636,7 +636,7 @@ static int __check_incompat_features(struct thin_disk_superblock *disk_super,
 	/*
 	 * Check for read-only metadata to skip the following RDWR checks.
 	 */
-	if (get_disk_ro(pmd->bdev->bd_disk))
+	if (bdev_read_only(pmd->bdev))
 		return 0;
 
 	features = le32_to_cpu(disk_super->compat_ro_flags) & ~THIN_FEATURE_COMPAT_RO_SUPP;