mfd: wm831x-spi: Add NULL check before pointer dereference

Add NULL check before dereferencing pointer of_id in order to avoid
a potential NULL pointer dereference.

Addresses-Coverity-ID: 1408830
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/wm831x-spi.c

@@ -34,6 +34,10 @@ static int wm831x_spi_probe(struct spi_device *spi)
 
 	if (spi->dev.of_node) {
 		of_id = of_match_device(wm831x_of_match, &spi->dev);
+		if (!of_id) {
+			dev_err(&spi->dev, "Failed to match device\n");
+			return -ENODEV;
+		}
 		type = (enum wm831x_parent)of_id->data;
 	} else {
 		type = (enum wm831x_parent)id->driver_data;