KVM: PPC: Fix HID5 setting code

The code to unset HID5.dcbz32 is broken.
This patch makes it do the right rotate magic.

Signed-off-by: Alexander Graf <agraf@suse.de>
Reported-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Avi Kivity <avi@redhat.com>