serial: fsl_lpuart: documented the clock requirement.

This is a correction to the documentation. It was previously required but not documented.

Signed-off-by: Yuan Yao <yao.yuan@freescale.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/fsl-lpuart.txt

@@ -4,6 +4,8 @@ Required properties:
 - compatible : Should be "fsl,<soc>-lpuart"
 - reg : Address and length of the register set for the device
 - interrupts : Should contain uart interrupt
+- clocks : phandle + clock specifier pairs, one for each entry in clock-names
+- clock-names : should contain: "ipg" - the uart clock
 
 Optional properties:
 - dmas: A list of two dma specifiers, one for each entry in dma-names.
@@ -17,6 +19,8 @@ uart0: serial@40027000 {
 		compatible = "fsl,vf610-lpuart";
 		reg = <0x40027000 0x1000>;
 		interrupts = <0 61 0x00>;
+		clocks = <&clks VF610_CLK_UART0>;
+		clock-names = "ipg";
 		dmas = <&edma0 0 2>,
 			<&edma0 0 3>;
 		dma-names = "rx","tx";