xfs/300: fix golden output

xfs/300: fix golden output

This test was written before a solution was in place, I think,
and so the expected output wasn't well tested.

The test does a loop of sparse writes from 6 to 0, but the
.out file expects 6 (not 7) extents.  Fix it.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>