Use DEVICE_ATTR_RO helper instead of plain DEVICE_ATTR,
which makes the code a bit shorter and easier to read.
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20210514081100.16196-1-yuehaibing@huawei.comSigned-off-by: Mark Brown <broonie@kernel.org>