arm64: dts: imx: imx8mn-beacon: Drop undocumented clock-names reference

The wlf,wm8962 Device Tree bindings do not specify a clock-names
property.  Drop it.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>