nios2: Convert to using %pOFn instead of device_node.name

In preparation to remove the node name pointer from struct device_node,
convert printf users to use the %pOFn format specifier.

Cc: Ley Foon Tan <lftan@altera.com>
Cc: nios2-dev@lists.rocketboards.org
Acked-by: Ley Foon Tan <ley.foon.tan@intel.com>
Signed-off-by: Rob Herring <robh@kernel.org>