to sbus_mdvec.dv_clock as sbus_mdvec.dv_clock is meant to be specified
in MHz. While this was a bug it shouldn't have affected FreeBSD/sparc64
as sbus_mdvec.dv_clock is used to limit the clock rate of chips when
a machine isn't able to support them at maximum speed which isn't the
case for sun4u machines.
- Remove the code that checks whether the clock frequency returned by
sbus_get_clockfreq() is 0 and falls back to 25MHz if it is as that's
already done in sbus(4).
Approved by: mjacob
MFC after: 3 days