oxnas: fix forgotten MTD partition name

Fixes: 858aebc0ef ("oxnas: unify MTD partition names")
Signed-off-by: Daniel Golle <[email protected]>

target/linux/oxnas/files/arch/arm/boot/dts/ox820-shuttle-kd20.dts

@@ -146,13 +146,13 @@
 		};
 
 		partition@40000 {
-			label = "uboot";
+			label = "u-boot";
 			reg = <0x00040000 0x001e0000>;
 			read-only;
 		};
 
 		partition@220000 {
-			label = "uboot_env";
+			label = "u-boot-env";
 			reg = <0x00220000 0x00020000>;
 		};