iio: frequency: adf4350: using an uninitialized variable

GCC complains that we use an uninitialized variable if the user passes
an invalid parameter to adf4350_read().  I decided that we should return
-EINVAL instead in that case.

However, when I looked up at adf4350_write() it returned -ENODEV for
that condition.  In the end, I decided the -EINVAL was the right thing
and I change adf4350_write() to match.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/iio/frequency/adf4350.c

@@ -272,7 +272,7 @@ static ssize_t adf4350_write(struct iio_dev *indio_dev,
 		adf4350_sync_config(st);
 		break;
 	default:
-		ret = -ENODEV;
+		ret = -EINVAL;
 	}
 	mutex_unlock(&indio_dev->mlock);
 
@@ -311,7 +311,7 @@ static ssize_t adf4350_read(struct iio_dev *indio_dev,
 		val = !!(st->regs[ADF4350_REG2] & ADF4350_REG2_POWER_DOWN_EN);
 		break;
 	default:
-		ret = -ENODEV;
+		ret = -EINVAL;
 	}
 	mutex_unlock(&indio_dev->mlock);