APEI / ERST: use 64-bit timestamps

32-bit timestamps are deprecated in the kernel, so we should not use
get_seconds(). In this case, the 'struct cper_record_header' structure
already contains a 64-bit field, so the only required change is to use
the safe ktime_get_real_seconds() interface as a replacement.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>