verific: Use new value change logic also for $stable of wide signals.

I missed this in the previous PR.

tests/sva/sva_value_change_changed_wide.sv

@@ -0,0 +1,22 @@
+module top (
+	input clk,
+	input [2:0] a,
+	input [2:0] b
+);
+	default clocking @(posedge clk); endclocking
+
+	assert property (
+		$changed(a)
+	);
+
+    assert property (
+        $changed(b) == ($changed(b[0]) || $changed(b[1]) || $changed(b[2]))
+    );
+
+`ifndef FAIL
+	assume property (
+		a !== 'x ##1 $changed(a)
+	);
+`endif
+
+endmodule