powerpc/macio: set a proper dma_coherent_mask

We have expected busses to set up a coherent mask to properly use the
common dma mapping code for a long time, and now that I've added a warning
macio turned out to not set one up yet.  This sets it to the same value
as the dma_mask, which seems to be what the drivers expect.
Reported-by: Mathieu Malaterre <malat@debian.org>
Tested-by: Mathieu Malaterre <malat@debian.org>
Reported-by: Meelis Roos <mroos@linux.ee>
Tested-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/macintosh/macio_asic.c

@@ -375,6 +375,7 @@ static struct macio_dev * macio_add_one_device(struct macio_chip *chip,
 	dev->ofdev.dev.of_node = np;
 	dev->ofdev.archdata.dma_mask = 0xffffffffUL;
 	dev->ofdev.dev.dma_mask = &dev->ofdev.archdata.dma_mask;
+	dev->ofdev.dev.coherent_dma_mask = dev->ofdev.archdata.dma_mask;
 	dev->ofdev.dev.parent = parent;
 	dev->ofdev.dev.bus = &macio_bus_type;
 	dev->ofdev.dev.release = macio_release_dev;