iio: adf4350: fix compiler warning [-Wuninitialized]

drivers/iio/frequency/adf4350.c:316:32: warning: ‘val’ may be used uninitialized in this function
[-Wuninitialized]
Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Reported-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/iio/frequency/adf4350.c

@@ -310,6 +310,8 @@ static ssize_t adf4350_read(struct iio_dev *indio_dev,
 	case ADF4350_PWRDOWN:
 		val = !!(st->regs[ADF4350_REG2] & ADF4350_REG2_POWER_DOWN_EN);
 		break;
+	default:
+		ret = -ENODEV;
 	}
 	mutex_unlock(&indio_dev->mlock);