sysfs: Fixup s390 sysfs files.

sysfs: Fixup s390 sysfs files.

- Remove count and off parameters from show() methods.
- Remove off parameter from store() methods.

Note 1: These have not been tested, but should be obviously correct.

Note 2: snprintf() was replaced with sprintf() where the filled buffer
would obviously be < PAGE_SIZE. (like when printing single integer values).
In places where strings were printed, PAGE_SIZE is used as the max string
size.