of/selftest: Use the resolver to fixup phandles

The selftest data ends up causing duplicate phandles in the live tree
for the time that the testcase data is inserted into the live tree. This
is obviously a bad situation because anything attempting to read the
tree while the selftests are running make resolve phandles to one of the
testcase data nodes. Fix the problem by using the of_resolve_phandles()
function to eliminate duplicates.

Signed-off-by: Grant Likely <grant.likely@linaro.org>
Cc: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Cc: Gaurav Minocha <gaurav.minocha.os@gmail.com>