The external clock frequency times the PLL multiplier may exceed the value
range of 32-bit unsigned integers. Instead perform the same calculation y
using two divisions.

The result has some potential to be different, but that's ok: this number
is used to limit the range of pre-PLL divisors to find optimal values. So
the effect of the rare case of a different result here would mean an
invalid pre-PLL divisor is tried. That will be found out a little later in
any case.

Also guard against dividing by zero if the external clock frequency is
higher than the maximum OP PLL output clock --- a rather improbable case.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>