fix oops in dma_unmap_page on not coherent mips platforms

[Jan Nikitenko <jan.nikitenko@gmail.com>]

dma_cache_wback_inv() expects virtual address, but physical was provided
due to translation via plat_dma_addr_to_phys().
If replaced with dma_addr_to_virt(), page fault oops from dma_unmap_page()
is gone on au1550 platform.

Signed-off-by: Jan Nikitenko <jan.nikitenko@gmail.com>
---
 arch/mips/mm/dma-default.c |    2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/mm/dma-default.c b/arch/mips/mm/dma-default.c
index 5b98d0e..5f336c1 100644
--- a/arch/mips/mm/dma-default.c
+++ b/arch/mips/mm/dma-default.c
@@ -222,7 +222,7 @@ void dma_unmap_page(struct device *dev, dma_addr_t 
dma_address, size_t size,
        if (!plat_device_is_coherent(dev) && direction != DMA_TO_DEVICE) {
                unsigned long addr;
 
-               addr = plat_dma_addr_to_phys(dma_address);
+               addr = dma_addr_to_virt(dma_address);
                dma_cache_wback_inv(addr, size);
        }