powerpc: Add missing reference to coherent_dma_mask

There is dma_mask in of_device upon of_platform_device_create()
but we don't actually set coherent_dma_mask. This may cause weird
behavior of USB subsystem using of_device USB host drivers.

Signed-off-by: Vitaly Bordug <vitb@kernel.crashing.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/powerpc/kernel/of_platform.c

@@ -76,6 +76,8 @@ struct of_device* of_platform_device_create(struct device_node *np,
 		return NULL;
 
 	dev->dma_mask = 0xffffffffUL;
+	dev->dev.coherent_dma_mask = DMA_32BIT_MASK;
+
 	dev->dev.bus = &of_platform_bus_type;
 
 	/* We do not fill the DMA ops for platform devices by default.