ASoC: max98088 - fix element type of the register cache.

The registers of max98088 are 8 bits, not 16 bits. This bug causes the
contents of registers to be overwritten with bad values when the codec
is suspended and then resumed.

Signed-off-by: Chih-Chung Chang <chihchung@chromium.org>
Signed-off-by: Dylan Reid <dgreid@chromium.org>
Signed-off-by: Mark Brown <broonie@linaro.org>
Cc: stable@vger.kernel.org