target-ppc: Update slb array with correct index values.

target-ppc: Update slb array with correct index values.

Without this, a value of rb=0 and rs=0 results in replacing the 0th
index. This can be observed when using gdb remote debugging support.

(gdb) x/10i do_fork
   0xc000000000085330 <do_fork>:        Cannot access memory at address 0xc000000000085330
(gdb)

This is because when we do the slb sync via kvm_cpu_synchronize_state,
we overwrite the slb entry (0th entry) for 0xc000000000085330

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Alexander Graf <agraf@suse.de>