at86rf230: init xtal_trim with zero

This patch initialize xtal_trim value to zero. The xtal_trim property is
an optional device tree value. Currently if no xtal_trim property is
given the xtal_trim value can be contain random data, because it's a
stack variable. This patch init the xtal_trim value to zero which is
also the default value after reset for at86rf230 transceivers.
Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

drivers/net/ieee802154/at86rf230.c

@@ -1572,7 +1572,7 @@ static int at86rf230_probe(struct spi_device *spi)
 	struct at86rf230_local *lp;
 	unsigned int status;
 	int rc, irq_type, rstn, slp_tr;
-	u8 xtal_trim;
+	u8 xtal_trim = 0;
 
 	if (!spi->irq) {
 		dev_err(&spi->dev, "no IRQ specified\n");