PM / devfreq: Convert to use sysfs_emit_at() API

Follow the advice of the Documentation/filesystems/sysfs.rst and show()
should only use sysfs_emit() or sysfs_emit_at() when formatting the
value to be returned to user space.

Link: https://lore.kernel.org/all/20231024183016.14648-3-ansuelsmth@gmail.com/
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>