s390/dasd: remove 'struct timespec' usage

getnstimeofday() and timespec are deprecated since they can
overflow on 32-bit architectures. This simply changes to the
explicitly typed timespec64 version that doesn't have that
problem.

It would be nice to also convert to monotonic timestamps
and call ktime_get_ts64() rather than ktime_get_real_ts64(),
but that would be a user-visible change.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Stefan Haberland <sth@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>