s390/cmf: read from hw buffer

To ensure data consistency when reading from the channel measurement
block we wait for the subchannel to become idle and copy the whole
block. This is unnecessary when all we do is export the individual
values via sysfs. Read the values for sysfs export directly from
the measurement block.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Reviewed-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>