Correctly convert the u64 arguments from 32bit to 64bit.

Pointed out by Heiko Carstens.

I guess this proves Linus' theory that nobody uses the more exotic Linux
specific syscalls.  It wasn't discovered by a user.
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>