Use DEVICE_ATTR_RO macro helper instead of plain DEVICE_ATTR, which makes
the code a bit shorter and easier to read.
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com> Signed-off-by: Lee Jones <lee.jones@linaro.org>