of: overlay: correctly apply overlay node with unit-address

Correct existing node name detection when overlay node name has
a unit-address.

Expected test result is overlay will update the nodes and properties
for /testcase-data-2/fairway-1/ride@100/ after this commit.

Before this commit:

   Console error message near end of unittest:
      OF: Duplicate name in fairway-1, renamed to "ride@100#1"

   $ cd /proc/device-tree/testcase-data-2/fairway-1/
   $ # extra node: ride@100#1
   $ ls
   #address-cells  linux,phandle   phandle         ride@200
   #size-cells     name            ride@100        status
   compatible      orientation     ride@100#1
   $ cd /proc/device-tree/testcase-data-2/fairway-1/ride@100/
   $ ls track@30/incline-up
   ls: track@30/incline-up: No such file or directory
   $ ls track@40/incline-up
   ls: track@40/incline-up: No such file or directory

After this commit:

   Console error message no longer occurs

   $ cd /proc/device-tree/testcase-data-2/fairway-1/
   $ # no extra node: ride@100#1
   $ ls
   #address-cells  compatible      name            phandle         ride@200
   #size-cells     linux,phandle   orientation     ride@100        status
   $ cd /proc/device-tree/testcase-data-2/fairway-1/ride@100/
   $ ls track@30/incline-up
   track@30/incline-up
   $ ls track@40/incline-up
   track@40/incline-up

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