csky: bugfix __pa(x) convert error.

videobuf2-dma-contig.c use dma_alloc get uncached direct-addr, and use
it to mmap for user-space.

The mmap use __pa(x) couldn't convert uncached direct-addr to phy-addr.

Signed-off-by: Guo Ren <ren_guo@c-sky.com>