ath79: specify "firmware" partition format for Ubiquiti UniFi

This affects:
1. Ubiquiti UniFi-AC-LITE/LR
2. Ubiquiti UniFi-AC-PRO
3. Ubiquiti UniFi-AC-MESH
4. Ubiquiti UniFi-AC-MESH PRO

Succesfully tested on UniFi AP AC Pro.

Signed-off-by: Rafał Miłecki <[email protected]>

target/linux/ath79/dts/qca9563_ubnt_unifiac.dtsi

@@ -82,6 +82,7 @@
 			partition@70000 {
 				label = "firmware";
 				reg = <0x070000 0x790000>;
+				compatible = "denx,uimage";
 			};
 
 			partition@800000 {