arch/x86/kernel/apic/apic_flat_64.c: Make comment match the code

Make the comment match the code, this also holds for intel systems,
according to probe_64.c in the same directory.

Signed-off-by: Jasper Spaans <spaans@fox-it.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>