dt-bindings: nfc: ti,trf7970a: fix usage example

The TRF7970A is a SPI device, not I2C.
Signed-off-by: Tobias Schramm <t.schramm@manjaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml

@@ -73,7 +73,7 @@ examples:
     #include <dt-bindings/gpio/gpio.h>
     #include <dt-bindings/interrupt-controller/irq.h>
 
-    i2c {
+    spi {
         #address-cells = <1>;
         #size-cells = <0>;