ARM: dts: stm32: fix AV96 board SAI2 pin muxing on stm32mp15

Replace sai2a-2 node name by sai2a-sleep-2, to avoid name
duplication.

Fixes: 1a9a9d22 ("ARM: dts: stm32: fix AV96 board SAI2 pin muxing on stm32mp15")
Signed-off-by: NOlivier Moysan <olivier.moysan@foss.st.com>
Signed-off-by: NAlexandre Torgue <alexandre.torgue@foss.st.com>

arch/arm/boot/dts/stm32mp15-pinctrl.dtsi

@@ -1246,7 +1246,7 @@
 		};
 	};
 
-	sai2a_sleep_pins_c: sai2a-2 {
+	sai2a_sleep_pins_c: sai2a-sleep-2 {
 		pins {
 			pinmux = <STM32_PINMUX('D', 13, ANALOG)>, /* SAI2_SCK_A */
 				 <STM32_PINMUX('D', 11, ANALOG)>, /* SAI2_SD_A */