ASoC: rx1950: Fix clkdiv for 16khz and 48khz

Usage of 256 as clkdiv gives better rounding error (<1%)
for 16khz and 48khz

Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>