media: solo6x10: use ktime_get_ts64() for time sync
solo6x10 correctly deals with time stamps and will never
suffer from overflows, but it uses the deprecated 'struct timespec'
type and 'ktime_get_ts()' interface to read the monotonic clock.
This changes it to use ktime_get_ts64() instead, so we can
eventually remove ktime_get_ts().