audit: use ktime_get_coarse_ts64() for time access

The API got renamed for consistency with the other time accessors,
this changes the audit caller as well.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>