powerpc/mpc8xxx DDR: Fix CAS latency calculation

Empty slot should be skipped when calculating CAS latency.

Signed-off-by: York Sun <yorksun@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>
diff --git a/arch/powerpc/cpu/mpc8xxx/ddr/lc_common_dimm_params.c b/arch/powerpc/cpu/mpc8xxx/ddr/lc_common_dimm_params.c
index a474a65..03a784c 100644
--- a/arch/powerpc/cpu/mpc8xxx/ddr/lc_common_dimm_params.c
+++ b/arch/powerpc/cpu/mpc8xxx/ddr/lc_common_dimm_params.c
@@ -27,8 +27,10 @@
 
 	/* compute the common CAS latency supported between slots */
 	tmp = dimm_params[0].caslat_X;
-	for (i = 1; i < number_of_dimms; i++)
-		 tmp &= dimm_params[i].caslat_X;
+	for (i = 1; i < number_of_dimms; i++) {
+		if (dimm_params[i].n_ranks)
+			tmp &= dimm_params[i].caslat_X;
+	}
 	common_caslat = tmp;
 
 	/* compute the max tAAmin tCKmin between slots */