fix byte-compile warning

I got following error when I byte-compiled.

```
Entering directory `/home/syohei/tmp/gomi/pos-tip/'

In pos-tip-w32-max-width-height:
pos-tip.el:944:25:Warning: `interactive-p' is an obsolete function (as of
    23.2); use `called-interactively-p' instead.
```