Fix CPU instruction Ld/St (single structure) with index != 0

ChocolArm64/Decoder/AOpCodeSimdMemSs.cs

@@ -82,6 +82,7 @@ namespace ChocolArm64.Decoder
                 }
             }
 
+            this.Index  = Index;
             this.SElems = SElems;
             this.Size   = Scale;