KVM: ppc: e500: Fix the bug that mas0 update to wrong value when read TLB entry

Should clear and then update the next victim area here.

Guest kernel only read TLB1 when startup kernel,
this bug result in an extra 4K TLB1 mapping in guest from 0x0 to 0x0.

As the problem has no impact to bootup a guest,
we didn't notice it before.

Signed-off-by: Liu Yu <yu.liu@freescale.com>
Signed-off-by: Avi Kivity <avi@redhat.com>