dt/bindings: Correct clk binding example for PIC32 serial.

Update binding example based on new clock binding scheme.
[1] Documentation/devicetree/bindings/clock/microchip,pic32.txt

Signed-off-by: Purna Chandra Mandal <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Cc: Kumar Gala <[e-mail]>
Cc: Ian Campbell <[e-mail]>
Cc: Joshua Henderson <[e-mail]>
Cc: Andrei Pistirica <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Patchwork: https://patchwork.linux-mips.org/patch/13267/
Signed-off-by: Ralf Baechle <[e-mail]>

Documentation/devicetree/bindings/serial/microchip,pic32-uart.txt

···
 		interrupts = <112 IRQ_TYPE_LEVEL_HIGH>,
 			<113 IRQ_TYPE_LEVEL_HIGH>,
 			<114 IRQ_TYPE_LEVEL_HIGH>;
-		clocks = <&PBCLK2>;
+		clocks = <&rootclk PB2CLK>;
 		pinctrl-names = "default";
 		pinctrl-0 = <&pinctrl_uart1
 				&pinctrl_uart1_cts