The previous sysfs change implies that the show() and store() methods in 
struct sysfs_ops are called only once, during the first read() or write().
This means that off is always 0, and count should always be PAGE_SIZE, to
fill or clear the entire buffer in one shot.

Therefore, those parameters can be removed from all attribute read/write 
methods. 

This changeset removes them from the definition and fixes sysfs to deal
with that appropriately.