s390/pai_ext: rework function paiext_copy argments

Change the function paiext_copy() parameter from a pointer to a
structure to two pointers to memory areas referenced. The other
members of that structure are not needed.

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Acked-by: Mete Durlu <meted@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>