of: unittest: Run overlay apply/revert sequence three times

Run the test for the overlay apply/revert sequence three times, to
test if there are unbalanced of_node_put() calls causing reference
counts to become negative.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/a9fb4eb560c58d11a7f167bc78a137b46e76cf15.1692699743.git.geert+renesas@glider.be


Signed-off-by: Rob Herring <robh@kernel.org>