clk: rk3399: Set empty for HCLK_SD assigned-clocks

Due to v5.7-rc1 sync the SD controller nodes in rk3399.dtsi
have HCLK_SD assigned-clocks which are usually required for
Linux and don't require to handle them in U-Boot.

 assigned-clocks = <&cru HCLK_SD>;

So, mark them as empty in clock otherwise device probe on
those SD controllers would fail.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/drivers/clk/rockchip/clk_rk3399.c b/drivers/clk/rockchip/clk_rk3399.c
index 1f62376..d822aca 100644
--- a/drivers/clk/rockchip/clk_rk3399.c
+++ b/drivers/clk/rockchip/clk_rk3399.c
@@ -996,6 +996,7 @@
 		break;
 	case ACLK_VOP1:
 	case HCLK_VOP1:
+	case HCLK_SD:
 		/**
 		 * assigned-clocks handling won't require for vopl, so
 		 * return 0 to satisfy clk_set_defaults during device probe.