Add fallback compatible string mdio-mux to fix below CHECK_DTBS warnings:
  arch/arm/boot/dts/nxp/ls/ls1021a-qds.dtb: mdio-mux-emi1 (mdio-mux-mmioreg): compatible: ['mdio-mux-mmioreg'] is too short
	from schema $id: http://devicetree.org/schemas/net/mdio-mux-mmioreg.yaml#

Signed-off-by: Frank Li <Frank.Li@nxp.com>
---
 arch/arm/boot/dts/nxp/ls/ls1021a-qds.dts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/boot/dts/nxp/ls/ls1021a-qds.dts b/arch/arm/boot/dts/nxp/ls/ls1021a-qds.dts
index 8bc8ff2e3b03d6eeb43d79fe0555842536ab735c..ce6e950ff10ea10b9431144e5147e75e3c0ce6cb 100644
--- a/arch/arm/boot/dts/nxp/ls/ls1021a-qds.dts
+++ b/arch/arm/boot/dts/nxp/ls/ls1021a-qds.dts
@@ -212,7 +212,7 @@ fpga: board-control@3,0 {
 		ranges = <0 3 0 0x100>;
 
 		mdio-mux-emi1 {
-			compatible = "mdio-mux-mmioreg";
+			compatible = "mdio-mux-mmioreg", "mdio-mux";
 			mdio-parent-bus = <&mdio0>;
 			#address-cells = <1>;
 			#size-cells = <0>;

-- 
2.34.1