samples: switch nrf overlays to sda-gpios, scl-gpios

I only see one sample with an overlay using the now legacy sda-pin and
scl-pin properties. Move it to the new style.

Signed-off-by: Martí Bolívar <[email protected]>

Author: mbolivar-nordic

samples/sensor/ccs811/boards/nrf51_ble400.overlay

@@ -6,8 +6,8 @@
 
 &i2c0 {
 	status = "okay";
-	sda-pin = <0>;
-	scl-pin = <1>;
+	sda-gpios = <&gpio0 0 0>;
+	scl-gpios = <&gpio0 1 0>;
 
 	/* Sparkfun Environment Combo uses second I2C address */
 	ccs811: ccs811@5b {