Fix ohci xfers for some devices by adjusting the number of microframes to a static value of 8.
Fix ohci xfers for some devices by adjusting the number of microframes to
a static value of 8.

Regression tested by todd@

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars