ASoC: max9850: remove unused variable 'max9850_reg'

sound/soc/codecs/max9850.c:31:33: warning:
 max9850_reg defined but not used [-Wunused-const-variable=]

It is not used since commit 06841662 ("ASoC:
max9850: Convert to direct regmap API usage")

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20190808143507.66788-1-yuehaibing@huawei.com


Signed-off-by: Mark Brown <broonie@kernel.org>