ARM: dts: exynos: Fix DTC unit name warnings in Exynos4x12

Fix following DTC warnings in Exynos4x12 boards:

Warning (unit_address_vs_reg): Node /camera/fimc-is@12000000/pmu has a reg or ranges property, but no unit name
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>

arch/arm/boot/dts/exynos4x12.dtsi

@@ -179,7 +179,7 @@ fimc_is: fimc-is@12000000 {
 			ranges;
 			status = "disabled";
 
-			pmu {
+			pmu@10020000 {
 				reg = <0x10020000 0x3000>;
 			};