s390/dasd: set timestamps unconditionally

Set the XRC timestamps even if XRC is not supported by the storage server
to help debugging the storage server firmware.
Do not advertise valid time stamps if the system time could not be
obtained.

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