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

On Tue, Nov 06, 2018 at 11:54:15AM +0000, Robin Murphy wrote:

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.

This looks good, but I think it could really use a comment as the use
of ret all the way down the function isn't exactly obvious.

Let me now if you want this picked up through the OF or DMA trees.