Note that the motion information includes subpel motion information

This was likely forgotten in 56bdf61b.

Tested:
```
$ make examples -j
...
$ doc/examples/extract_mvs in.264 | head -40 | \
    csvcut -C framenum,source,flags |csvlook
| blockw | blockh |  srcx | srcy |  dstx | dsty | motion_x | motion_y | motion_scale |
| ------ | ------ | ----- | ---- | ----- | ---- | -------- | -------- | ------------ |
|     16 |     16 |    20 |   26 |     8 |    8 |       49 |       72 |            4 |
|     16 |     16 |   152 |   15 |   136 |    8 |       65 |       28 |            4 |
|     16 |      8 |   360 |    3 |   360 |    4 |        1 |       -6 |            4 |
|     16 |      8 |   360 |   13 |   360 |   12 |       -1 |        4 |            4 |
|     16 |     16 |   440 |   10 |   440 |    8 |        3 |       10 |            4 |
|      8 |     16 |   829 |    7 |   836 |    8 |      -31 |       -6 |            4 |
|      8 |     16 |   844 |    7 |   844 |    8 |       -1 |       -4 |            4 |
|     16 |     16 | 1,004 |   14 | 1,048 |    8 |     -177 |       24 |            4 |
|     16 |     16 | 1,096 |    8 | 1,096 |    8 |       -1 |        0 |            4 |
|     16 |      8 | 1,417 |   24 | 1,416 |    4 |        7 |       82 |            4 |
|     16 |      8 | 1,416 |   13 | 1,416 |   12 |        0 |        6 |            4 |
|     16 |      8 |    87 |   20 |    88 |   20 |       -7 |        0 |            4 |
|     16 |      8 |    99 |   44 |    88 |   28 |       45 |       66 |            4 |
...
```

Also:
```
$ make fate -j
...
```
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>