xfs: consolidate xfs_inumbers

From: Jie Liu <jeff.liu@oracle.com>

Consolidate xfs_inumbers() to make the formatter function return correct
error and make the source code looks a bit neat.

Signed-off-by: Jie Liu <jeff.liu@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>