powerpc/64s/hash: Fix stab_rr off by one initialization

This causes SLB alloation to start 1 beyond the start of the SLB.
There is no real problem because after it wraps it stats behaving
properly, it's just surprisig to see when looking at SLB traces.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/mm/slb.c

@@ -425,7 +425,7 @@ void slb_initialize(void)
 #endif
 	}
 
-	get_paca()->stab_rr = SLB_NUM_BOLTED;
+	get_paca()->stab_rr = SLB_NUM_BOLTED - 1;
 
 	lflags = SLB_VSID_KERNEL | linear_llp;
 	vflags = SLB_VSID_KERNEL | vmalloc_llp;