ASoC: wm5110: Add FSH for ISRCs

Currently, the driver only supports configuration of the lower sample
rate (FSL) on the ISRCs. With the higher rate being fixed a SYSCLK, this
patch adds support for configuring the higher sample rate (FSH).

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@linaro.org>