of: Add a testcase for of_find_node_by_path()

Add a testcase for the find_node_by_path() function to make sure it
handles all the valid scenarios.

Signed-off-by: Grant Likely <grant.likely@linaro.org>

diff --cc drivers/of/selftest.c
Simple merge

diff --cc drivers/of/testcase-data/tests-phandle.dtsi
Simple merge