overlays: pi3-disable-bt: Clear out bt_pins node

The pi3-disable-bt overlay does not (and cannot) delete the bt_pins
node, but emptying its properties (including brcm,pins) is a way of
signalling to the hciuart systemd service that Bluetooth has been
disabled.

Signed-off-by: Phil Elwell <phil@raspberrypi.org>
Signed-off-by: ahmedradaideh <ahmed.radaideh@gmail.com>

arch/arm/boot/dts/overlays/pi3-disable-bt-overlay.dts

@@ -37,6 +37,15 @@
 	};
 
 	fragment@3 {
+		target = <&bt_pins>;
+		__overlay__ {
+			brcm,pins;
+			brcm,function;
+			brcm,pull;
+		};
+	};
+
+	fragment@4 {
 		target-path = "/aliases";
 		__overlay__ {
 			serial0 = "/soc/serial@7e201000";