soc/tegra: fuse: Fix reading registers using DMA on Tegra20

FUSE driver doesn't configure DMA channel properly, because of it DMA
transfer is never issued and tegra20_fuse_read() always return 0x0.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>