arm64: dts: rockchip: set codec system-clock-fixed on px30-ringneck-haikou

Having sgtl5000_clk defines as "fixed-clock" is not enough to prevent
the dai subsystem from overwriting the frequency via sgtl5000_set_dai_sysclk.

Setting system-clock-fixed does the job, and now a 1kHz sine wave
comes out as actually 1kHz, no matter the sample rate of the source.

Testcase: These should sound the same:

 speaker-test -r 48000 -t sine -f 1000
 speaker-test -r 24000 -t sine -f 1000

Also remove the clock link here as having it in sgtl5000 and
sgtl5000_codec causes duplicate clock unprepares with associated
backtrace.

Cc: [email protected]
Fixes: c484cf9 ("arm64: dts: rockchip: add PX30-µQ7 (Ringneck) SoM with Haikou baseboard")
Signed-off-by: Jakob Unterwurzacher <[email protected]>
Link: https://lore.kernel.org/r/20230907151725.198347-2-jakob.unterwurzacher@theobroma-systems.com
Signed-off-by: Heiko Stuebner <[email protected]>

Author: rfjakob

arch/arm64/boot/dts/rockchip/px30-ringneck-haikou.dts

@@ -72,8 +72,10 @@
 		simple-audio-card,bitclock-master = <&sgtl5000_codec>;
 
 		sgtl5000_codec: simple-audio-card,codec {
-			clocks = <&sgtl5000_clk>;
 			sound-dai = <&sgtl5000>;
+			// Prevent the dai subsystem from overwriting the clock
+			// frequency. We are using a fixed-frequency oscillator.
+			system-clock-fixed;
 		};
 
 		simple-audio-card,cpu {