ACPI: sysfs: evaluate _STR on each sysfs access

The handling of the _STR method is inconsistent with the other method
evaluations. It is the only method which is cached.

The cached value stored in 'struct acpi_device_pnp' has a different
lifetime than the other struct members.

Commit d1efe3c3 ("ACPI: Add new sysfs interface to export device description")
does not explain this difference.

Evaluating the method every time also removes the necessity to manage
the lifetime of the cached value, which would be a problem when managing
the sysfs attributes through the device core.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://patch.msgid.link/20240709-acpi-sysfs-groups-v2-2-058ab0667fa8@weissschuh.net


Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>