test: clk: test clock self assignment

Make sure that the clock self-assignment works by having a clock of
clk-sbox be configured automatically when clk-sbox is probed.

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
diff --git a/arch/sandbox/dts/test.dts b/arch/sandbox/dts/test.dts
index a5b9fbd..fdb08f2 100644
--- a/arch/sandbox/dts/test.dts
+++ b/arch/sandbox/dts/test.dts
@@ -226,6 +226,8 @@
 	clk_sandbox: clk-sbox {
 		compatible = "sandbox,clk";
 		#clock-cells = <1>;
+		assigned-clocks = <&clk_sandbox 3>;
+		assigned-clock-rates = <321>;
 	};
 
 	clk-test {