[S390] hibernate: Use correct place for CPU address in lowcore

We used address 0x1084 instead of 0x84 to store the suspend CPU address.
With this patch we use the correct address 0x84 as it is defined in
the POP.

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>