clk: sandbox: add composite clk

Add composite clk to sandbox driver

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/include/sandbox-clk.h b/include/sandbox-clk.h
index 37c9838..f449de1 100644
--- a/include/sandbox-clk.h
+++ b/include/sandbox-clk.h
@@ -19,6 +19,7 @@
 	SANDBOX_CLK_ECSPI1,
 	SANDBOX_CLK_USDHC1_SEL,
 	SANDBOX_CLK_USDHC2_SEL,
+	SANDBOX_CLK_I2C,
 };
 
 enum sandbox_pllv3_type {