ARM: dts: stm32: fix ltdc pinctrl on microdev2.0-of7

It prevents the following warning:

 pin-controller@50002000: 'ltdc' does not match any of the regexes:
'-[0-9]*$', '^gpio@[0-9a-f]*$', 'pinctrl-[0-9]+'
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>

arch/arm/boot/dts/stm32mp157a-microgea-stm32mp1-microdev2.0-of7.dts

@@ -89,7 +89,7 @@ ltdc_ep0_out: endpoint@0 {
 };
 
 &pinctrl {
-	ltdc_pins: ltdc {
+	ltdc_pins: ltdc-0 {
 		pins {
 			pinmux = <STM32_PINMUX('G', 10, AF14)>,	/* LTDC_B2 */
 				 <STM32_PINMUX('H', 12, AF14)>,	/* LTDC_R6 */