x86: return correct error code from child_rip in x86_64 entry.S

Right now register edi is just cleared before calling do_exit.
That is wrong because correct return value will be ignored.
Value from rax should be copied to rdi instead of clearing edi.

AK: changed to 32bit move because it's strictly an int

[ tglx: arch/x86 adaptation ]

Signed-off-by: Andrey Mirkin <major@openvz.org>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>