ARM: dts: stm32: fix display pinmux for stm32f746-disco

As reported by the datasheet (DocID027590 Rev 4) for PG12:
- AF9  -> LCD_B4
- AF14 -> LCD_B1

So replace AF14 with AF9 for PG12 in the dts.

Fixes: fe63d3cfb77ef ("ARM: dts: stm32: Sync DT with v4.20 kernel for stm32f7")
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
diff --git a/arch/arm/dts/stm32f746-disco-u-boot.dtsi b/arch/arm/dts/stm32f746-disco-u-boot.dtsi
index 19b5451..522cffb 100644
--- a/arch/arm/dts/stm32f746-disco-u-boot.dtsi
+++ b/arch/arm/dts/stm32f746-disco-u-boot.dtsi
@@ -169,7 +169,7 @@
 	ltdc_pins: ltdc@0 {
 		pins {
 			pinmux = <STM32_PINMUX('E', 4, AF14)>, /* B0 */
-				 <STM32_PINMUX('G',12, AF14)>, /* B4 */
+				 <STM32_PINMUX('G',12, AF9)>,  /* B4 */
 				 <STM32_PINMUX('I', 9, AF14)>, /* VSYNC */
 				 <STM32_PINMUX('I',10, AF14)>, /* HSYNC */
 				 <STM32_PINMUX('I',14, AF14)>, /* CLK */