of: overlay: do not duplicate properties from overlay for new nodes

When allocating a new node, add_changeset_node() was duplicating the
properties from the respective node in the overlay instead of
allocating a node with no properties.

When this patch is applied the errors reported by the devictree
unittest from patch "of: overlay: add tests to validate kfrees from
overlay removal" will no longer occur.  These error messages are of
the form:

   "OF: ERROR: ..."

and the unittest results will change from:

   ### dt-test ### end of unittest - 203 passed, 7 failed

to

   ### dt-test ### end of unittest - 210 passed, 0 failed

Tested-by: Alan Tull <atull@kernel.org>
Signed-off-by: Frank Rowand <frank.rowand@sony.com>