VFM: Fix value of VFMMatch property

It was reporting the matches used for the two interlaced frames
in a cycle as "0" whether the field parameter was 0 or 1 (order=1
in both cases). TFM reports "n" when field is 0 and "p" when field
is 1.
Merge pull request #74 from dubhater/vfm_bug

VFM: Fix value of VFMMatch property