staging:iio:dac:ad5504: Check if IRQ was requested before freeing it

IRQ support is optional, so we have to check whether it was actually requested
before we attempt to free it.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/iio/dac/ad5504.c

@@ -294,7 +294,8 @@ static int __devinit ad5504_probe(struct spi_device *spi)
 	return 0;
 
 error_free_irq:
-	free_irq(spi->irq, indio_dev);
+	if (spi->irq)
+		free_irq(spi->irq, indio_dev);
 error_disable_reg:
 	if (!IS_ERR(reg))
 		regulator_disable(reg);