KVM: PPC: Make XER load 32 bit

We have a 32 bit value in the PACA to store XER in. We also do an stw
when storing XER in there. But then we load it with ld, completely
screwing it up on every entry.

Welcome to the Big Endian world.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>