documentation: drivers/core/of: fix name of of_node symlink

commit 5590f319

 ("drivers/core/of: Add symlink to device-tree from
devices with an OF node") added a symlink called "of_node" to sysfs
however the documentation describes it as "of_path".

Fix the documentation to match what the code actually does.

Signed-off-by: Martin Fuzzey <mfuzzey@parkeon.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>