ASoC: sgtl5000: Fix wrong mask in some snd_soc_update_bits calls

Ensure all mask bits are clear before setting new value.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Dong Aisheng <b29396@freescale.com>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>