ARM: dts: stm32: add system-clock-direction-out on stm32mp15xx-dkx

The commit 5725bce709db
("ASoC: simple-card-utils: Unify clock direction by clk_direction")
corrupts the audio on STM32MP15 DK sound cards.
The parent clock is not correctly set, because set_sai_ck_rate() is not
executed in stm32_sai_set_sysclk() callback.
This occurs because set_sysclk() is called with the wrong direction,
SND_SOC_CLOCK_IN instead of SND_SOC_CLOCK_OUT.

Add system-clock-direction-out property in SAI2A endpoint node of
STM32MP15XX-DKX device tree, to specify the MCLK clock direction.

Signed-off-by: Olivier Moysan <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexandre Torgue <[e-mail]>

arch/arm/boot/dts/st/stm32mp15xx-dkx.dtsi

···
 				remote-endpoint = <&cs42l51_tx_endpoint>;
 				dai-format = "i2s";
 				mclk-fs = <256>;
+				system-clock-direction-out;
 				dai-tdm-slot-num = <2>;
 				dai-tdm-slot-width = <32>;
 			};