s390/hwsampler: Updated misleading member names in hws_data_entry

There is a misleading naming of the program parameter fields, so
correct them according to their names as outlined in
"The Load-Program-Parameter and the CPU-measurement Facilities"
(SA23-2260-03).

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>