btrfs: add blake2b to checksumming algorithms

Add blake2b (with 256 bit digest) to the list of possible checksumming
algorithms used by BTRFS.

Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -354,6 +354,7 @@ static bool btrfs_supported_super_csum(u16 csum_type)
 	case BTRFS_CSUM_TYPE_CRC32:
 	case BTRFS_CSUM_TYPE_XXHASH:
 	case BTRFS_CSUM_TYPE_SHA256:
+	case BTRFS_CSUM_TYPE_BLAKE2:
 		return true;
 	default:
 		return false;