memory: tegra{20,30}-mc: Fix reading incorrect register in mc_readl()

The code reading the register does not match the code writing to the register,
fix it.

Also fix the coding style in mc_writel() for better readability.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>