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

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: Linus Walleij <[e-mail]>
Cc: Kumar Gala <[e-mail]>
Cc: Ian Campbell <[e-mail]>
Cc: [e-mail]
Cc: Mark Rutland <[e-mail]>
Cc: Alexandre Courbot <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Patchwork: https://patchwork.linux-mips.org/patch/13270/
Signed-off-by: Ralf Baechle <[e-mail]>

Documentation/devicetree/bindings/gpio/microchip,pic32-gpio.txt

···
 	gpio-controller;
 	interrupt-controller;
 	#interrupt-cells = <2>;
-	clocks = <&PBCLK4>;
+	clocks = <&rootclk PB4CLK>;
 	microchip,gpio-bank = <0>;
 	gpio-ranges = <&pic32_pinctrl 0 0 16>;
 };