Arm: dts: stm32: remove extra compatible string for uart

This patch removes the extra compatibility string "st,stm32-usart" to
avoid confusion, save some time & space.

Signed-off-by: Vikas Manocha <[e-mail]>
Reviewed-by: Patrice Chotard <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/devicetree/bindings/dma/stm32-dma.txt

···
 Example:
 
 	usart1: serial@40011000 {
-		compatible = "st,stm32-usart", "st,stm32-uart";
+		compatible = "st,stm32-uart";
 		reg = <0x40011000 0x400>;
 		interrupts = <37>;
 		clocks = <&clk_pclk2>;

Documentation/devicetree/bindings/serial/st,stm32-usart.txt

···
 
 Required properties:
 - compatible: can be either:
-  - "st,stm32-usart",
   - "st,stm32-uart",
-  - "st,stm32f7-usart",
   - "st,stm32f7-uart",
-  - "st,stm32h7-usart"
   - "st,stm32h7-uart".
-  depending on whether the device supports synchronous mode
-  and is compatible with stm32(f4), stm32f7 or stm32h7.
+  depending is compatible with stm32(f4), stm32f7 or stm32h7.
 - reg: The address and length of the peripheral registers space
 - interrupts:
   - The interrupt line for the USART instance,
···
 };
 
 usart2: serial@40004400 {
-	compatible = "st,stm32-usart", "st,stm32-uart";
+	compatible = "st,stm32-uart";
 	reg = <0x40004400 0x400>;
 	interrupts = <38>;
 	clocks = <&clk_pclk1>;
···
 };
 
 usart1: serial@40011000 {
-	compatible = "st,stm32-usart", "st,stm32-uart";
+	compatible = "st,stm32-uart";
 	reg = <0x40011000 0x400>;
 	interrupts = <37>;
 	clocks = <&rcc 0 164>;