wrong return from machine_rp2_pwm.go Period

[miroslavristic]

There is an error at the end of Period function causing wrong return from the function.

Last line of the function is:
return (16uint64(Int) + uint64(frac)) * uint64((top+1)(phc+1)1e9) / (16 * freq) // cycles = (TOP+1) * (CSRPHCorrect + 1) * (DIV_INT + DIV_FRAC/16)
The issue is caused by overflow in:
uint64((top+1)(phc+1)*1e9)

The fix is simple, the line should be:
return (16uint64(Int) + uint64(frac)) * uint64((top+1)(phc+1)) * uint64(1e9) / (16 * freq) // cycles = (TOP+1) * (CSRPHCorrect + 1) * (DIV_INT + DIV_FRAC/16)

[dgryski]

/cc @soypat

[soypat]

Thank you @miroslavristic for reporting and @dgryski for tagging me.

See #5165