ARM: dts: exynos: fix WM8960 clock name in Itop Elite

The WM8960 Linux driver expects the clock to be named "mclk".  Otherwise
the clock will be ignored and not prepared/enabled by the driver.

Cc: <stable@vger.kernel.org>
Fixes: 339b2fb3

 ("ARM: dts: exynos: Add TOPEET itop elite based board")
Link: https://lore.kernel.org/r/20230217150627.779764-3-krzysztof.kozlowski@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>