of: overlay: remove a dependency on device node full_name

The "%pOF" printf format was recently added to print the
full name of a device tree node, with the intent of changing
the node full_name field to contain only the node name instead
of the full path of the node.

dup_and_fixup_symbol_prop() duplicates a property from the
"/__symbols__" node of an overlay device tree.  The value
of each duplicated property must be fixed up to include
the full path of a node in the live device tree.  The
current code uses the node's full_name for that purpose.
Update the code to use the "%pOF" printf format to
determine the node's full path.

Signed-off-by: Frank Rowand <frank.rowand@sony.com>
Signed-off-by: Rob Herring <robh@kernel.org>