sparc: prom: use property "name" directly to construct node names

In preparation to remove direct accesses to the device_node.name
pointer, retrieve the node name from the "name" property instead. This
is slightly less optimal as we have to walk the kernel's DT property
list to find the "name" property.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: sparclinux@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>