liquidio: use ktime_get_real_ts64() instead of getnstimeofday64()

The two do the same thing, but we want to have a consistent
naming in the kernel.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Felix Manlunas <felix.manlunas@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>