arm64: dts: rockchip: Drop invalid mic-in-differential on rk3568-rock-3a

The 'mic-in-differential' DT property supported by the RK809/RK817 audio
codec driver is actually valid if prefixed with 'rockchip,':

  DTC_CHK arch/arm64/boot/dts/rockchip/rk3568-rock-3a.dtb
  rk3568-rock-3a.dtb: pmic@20: codec: 'mic-in-differential' does not match any of the regexes: 'pinctrl-[0-9]+'
	from schema $id: http://devicetree.org/schemas/mfd/rockchip,rk809.yaml#

However, the board doesn't make use of differential signaling, hence
drop the incorrect property and the now unnecessary 'codec' node.

Fixes: 22a442e6 ("arm64: dts: rockchip: add basic dts for the radxa rock3 model a")
Reported-by: Jonas Karlman <jonas@kwiboo.se>
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Link: https://lore.kernel.org/r/20240622-rk809-fixes-v2-3-c0db420d3639@collabora.comSigned-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm64/boot/dts/rockchip/rk3568-rock-3a.dts

@@ -531,10 +531,6 @@ regulator-state-mem {
 				};
 			};
 		};
-
-		codec {
-			mic-in-differential;
-		};
 	};
 };