ASoC: PLL computation in TLV320AIC3x SoC driver

fix precision of PLL computation for TLV320AIC3x SoC driver,
test results are at http://pmeerw.net/clk

Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
Acked-by: Vladimir Barinov <vova.barinov@gmail.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>