ASoC: core: Allow snd_soc_update_bits use 32 bits register

Change reg's type from unsigned short to unsigned int. So that we can use
32 bits reg value in snd_soc_update_bits.

Signed-off-by: Bard Liao <bardliao@realtek.com>
Signed-off-by: Mark Brown <broonie@linaro.org>