gcc 7.4.0 build fails:

In file included from sound/soc/amd/acp3x-rt5682-max9836.c:20:0:
sound/soc/amd/raven/acp3x.h: In function rv_readl:
sound/soc/amd/raven/acp3x.h:113:9: error: implicit declaration of function readl; did you mean rv_readl? [-Werror=implicit-function-declaration]
  return readl(base_addr - ACP3x_PHY_BASE_ADDRESS);
         ^~~~~
         rv_readl
sound/soc/amd/raven/acp3x.h: In function rv_writel:
sound/soc/amd/raven/acp3x.h:118:2: error: implicit declaration of function writel; did you mean rv_writel? [-Werror=implicit-function-declaration]
  writel(val, base_addr - ACP3x_PHY_BASE_ADDRESS);
  ^~~~~~
  rv_writel

Add <linux/io.h> to fix this.

Fixes: 6b8e4e7d ("ASoC: amd: Add machine driver for Raven based platform")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Message-Id: <20200304084057.44764-1-yuehaibing@huawei.com>
Signed-off-by: Mark Brown <broonie@kernel.org>