xfs_db: associate proper type with free inode btree root

xfs_db: associate proper type with free inode btree root

When navigating to the free inode btree root, the wrong type
is set:

xfs_db> agi 0
xfs_db> addr free_root
xfs_db> type
current type is "inobt"

Change this to type finobt / TYP_FINOBT

(There seems to be no actual difference, but if we have an explicit type
name for the free inode btree, we should use it as appropriate)

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>