of/device: Really only set bus DMA mask when appropriate

of_dma_configure() was *supposed* to be following the same logic as
acpi_dma_configure() and only setting bus_dma_mask if some range was
specified by the firmware. However, it seems that subtlety got lost in
the process of fitting it into the differently-shaped control flow, and
as a result the force_dma==true case ends up always setting the bus mask
to the 32-bit default, which is not what anyone wants.

Make sure we only touch it if the DT actually said so.

Fixes: 6c2fb2ea ("of/device: Set bus DMA mask as appropriate")
Reported-by: NAaro Koskinen <aaro.koskinen@iki.fi>
Reported-by: NJean-Philippe Brucker <jean-philippe.brucker@arm.com>
Tested-by: NAaro Koskinen <aaro.koskinen@iki.fi>
Tested-by: NJohn Stultz <john.stultz@linaro.org>
Tested-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Tested-by: NRobert Richter <robert.richter@cavium.com>
Signed-off-by: NRobin Murphy <robin.murphy@arm.com>
Signed-off-by: NRob Herring <robh@kernel.org>

drivers/of/device.c

@@ -149,9 +149,11 @@ int of_dma_configure(struct device *dev, struct device_node *np, bool force_dma)
 	 * set by the driver.
 	 */
 	mask = DMA_BIT_MASK(ilog2(dma_addr + size - 1) + 1);
-	dev->bus_dma_mask = mask;
 	dev->coherent_dma_mask &= mask;
 	*dev->dma_mask &= mask;
+	/* ...but only set bus mask if we found valid dma-ranges earlier */
+	if (!ret)
+		dev->bus_dma_mask = mask;
 
 	coherent = of_dma_is_coherent(np);
 	dev_dbg(dev, "device is%sdma coherent\n",