hwmon: Use device_show_string() helper for sysfs attributes

hwmon: Use device_show_string() helper for sysfs attributes

Deduplicate sysfs ->show() callbacks which expose a string at a static
memory location.  Use the newly introduced device_show_string() helper
in the driver core instead by declaring those sysfs attributes with
DEVICE_STRING_ATTR_RO().

No functional change intended.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/23c2031acaa64f1c02f00e817c3f7e4466d17ab2.1713608122.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>