staging:iio:ad799x fix error_free_irq which was freeing an irq that may not have been requested

Only free an IRQ in error_free_irq, if it has been requested previously.
Signed-off-by: Hartmut Knaack <knaack.h@gmx.de>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Cc: stable@vger.kernel.org

drivers/staging/iio/adc/ad799x_core.c

@@ -594,7 +594,8 @@ static int ad799x_probe(struct i2c_client *client,
 	return 0;
 
 error_free_irq:
-	free_irq(client->irq, indio_dev);
+	if (client->irq > 0)
+		free_irq(client->irq, indio_dev);
 error_cleanup_ring:
 	ad799x_ring_cleanup(indio_dev);
 error_disable_reg: