Nullify spread spectrum

[mrguen]

Describe the bug

On some chips the frequency seems wrong. In fact when checking the registers spread spectrum was activated. Probably from the factory.

Correction

I added code in the reset() function

void Si5351::reset(void) {
...
	si5351_write(SI5351_SSC_PARAM0, 0);
	si5351_write(SI5351_SSC_PARAM1, 0);
	si5351_write(SI5351_SSC_PARAM2, 0);
	si5351_write(SI5351_SSC_PARAM3, 0);
	si5351_write(SI5351_SSC_PARAM4, 0);
	si5351_write(SI5351_SSC_PARAM5, 0);
	si5351_write(SI5351_SSC_PARAM6, 0);
	si5351_write(SI5351_SSC_PARAM7, 0);
	si5351_write(SI5351_SSC_PARAM8, 0);
	si5351_write(SI5351_SSC_PARAM9, 0);
	si5351_write(SI5351_SSC_PARAM10, 0);
	si5351_write(SI5351_SSC_PARAM11, 0);
	si5351_write(SI5351_SSC_PARAM12, 0);
...
}