s390/dasd: avoid calling do_gettimeofday()

do_gettimeofday() is deprecated because it's not y2038-safe on
32-bit architectures. Since it is basically a wrapper around
ktime_get_real_ts64(), we can just call that function directly
instead.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[sth@linux.vnet.ibm.com: fix build]
Signed-off-by: Stefan Haberland <sth@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>