Neither spdif_src nor spdif_pll exists, judging by the vendor kernel in
both cases spdif_pre was meant. This brings the naming in line and
hierachy in line with that of sclk_i2s0.
Also allow sclk_spdif and spdif_frac to change their parents rate as
that the upstream dividers are purely there to feed sclk_spdif