s390/cpumf: remove 60 seconds read limit

Remove the 60 seconds read interval limit. Do not impose any limit
at all and allow read of complete counter sets.

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>