Upgrade the default scroll distance to 120

This is just a number, to be used as divider and shouldn't have any effect in
correctly written clients. With the high-res scrolling coming up however, we
have a few devices where the dist cannot be expressed as an integer fraction
of 15, so let's up it to 120 because we know all hardware wheels have to be an
integer fraction of that that, thanks to Microsoft's API requirements.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>