[PATCH powerpc] Revert c6102609 and replace it with the correct fix for vio dma mask setting

[Li Zhong <zhong@linux.vnet.ibm.com>]

This patch reverts my previous "fix", and replace it with the correct
fix from Russell. 

And as Russell pointed out -- dma_set_mask_and_coherent() (and the other
dma_set_mask() functions) are really supposed to be used by drivers
only.

Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/vio.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/vio.c b/arch/powerpc/kernel/vio.c
index 76a6482..d771778 100644
--- a/arch/powerpc/kernel/vio.c
+++ b/arch/powerpc/kernel/vio.c
@@ -1419,7 +1419,8 @@ struct vio_dev *vio_register_device_node(struct device_node *of_node)
 
 		/* needed to ensure proper operation of coherent allocations
 		 * later, in case driver doesn't set it explicitly */
-		dma_coerce_mask_and_coherent(&viodev->dev, DMA_BIT_MASK(64));
+		viodev->dev.coherent_dma_mask = DMA_BIT_MASK(64);
+		viodev->dev.dma_mask = &viodev->dev.coherent_dma_mask;
 	}
 
 	/* register with generic device framework */