libgfs2: Return the inode from build_quota()
    
    This allows the caller to call inode_put() when it's convenient and also
    allows the debug message printing to be moved out of the function.
    fsck.gfs2 passes the function by reference so it needs a shim until the
    other builder functions can be given the same signature.
    
    Signed-off-by: Andrew Price <anprice@redhat.com>