ARM: dts: exynos: Align MAX77836 nodes with dtschema on Monk and Rinato

The newly introduced dtschema for MAX77836 MUIC requires proper naming
of extcon child node.

This should not have actual impact on MFD children driver binding,
because the max77836 MFD driver uses compatibles.

Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/arm/boot/dts/exynos3250-monk.dts

···
 			reg = <0x25>;
 			wakeup-source;
 
-			muic: max77836-muic {
+			extcon {
 				compatible = "maxim,max77836-muic";
 			};
 

arch/arm/boot/dts/exynos3250-rinato.dts

···
 			reg = <0x25>;
 			wakeup-source;
 
-			muic: max77836-muic {
+			extcon {
 				compatible = "maxim,max77836-muic";
 			};