ARM: dts: exynos: align STMPE ADC node name with bindings in P4 Note

The node name should be generic thus rename STMPE ADC child to "adc".
Bindings will expect such name as well.

Link: https://lore.kernel.org/r/20230225164050.42522-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>