clamp_mvs() using the wrong motion vector information

In the "Removed bmi copy to/from BLOCKD" commit, the copy
to the bmi in BLOCKD was eliminated.  The clamp_mvs() used
the bmi in BLOCKD, which now contains incorrect values.  This
patch fixes this problem.

Change-Id: I8eca1eaf4015052b0b63e90876f7ad321aba7cff