powerpc/corenet: explicitly disable the SDHC controller on kmcoge4

It is not implemented on the kmcoge4 hardware and if not disabled it
leads to error messages with the corenet32_smp_defconfig.
Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
Signed-off-by: Scott Wood <oss@buserror.net>

arch/powerpc/boot/dts/fsl/kmcoge4.dts

@@ -83,6 +83,10 @@ flash@2 {
 			};
 		};
 
+		sdhc@114000 {
+			status = "disabled";
+		};
+
 		i2c@119000 {
 			status = "disabled";
 		};