serial: stm32x7: remove stm32f7-usart and stm32h7-usart compatible

This patch remove the extra compatibility string "st,stm32h7-usart"
and "st,stm32f7-usart" to avoid confusion, save some time & space.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Vikas Manocha <vikas.manocha@st.com>
diff --git a/arch/arm/dts/stm32h743.dtsi b/arch/arm/dts/stm32h743.dtsi
index 16e9308..a413866 100644
--- a/arch/arm/dts/stm32h743.dtsi
+++ b/arch/arm/dts/stm32h743.dtsi
@@ -76,7 +76,7 @@
 		};
 
 		usart1: serial@40011000 {
-			compatible = "st,stm32h7-usart", "st,stm32h7-uart";
+			compatible = "st,stm32h7-uart";
 			reg = <0x40011000 0x400>;
 			interrupts = <37>;
 			status = "disabled";
@@ -84,7 +84,7 @@
 		};
 
 		usart2: serial@40004400 {
-			compatible = "st,stm32h7-usart", "st,stm32h7-uart";
+			compatible = "st,stm32h7-uart";
 			reg = <0x40004400 0x400>;
 			interrupts = <38>;
 			status = "disabled";