of: overlay: unittest: overlay_bad_unresolved: Spelling s/ok/okay/

While "ok" is recognized, the proper status value for an operational
device is "okay".

Fixes: eb38b9529aefa344 ("of: overlay: unittest: Add test for unresolved symbol")
Signed-off-by: Geert Uytterhoeven <[e-mail]>
Link: https://lore.kernel.org/r/923f4[e-mail]
Signed-off-by: Rob Herring <[e-mail]>

drivers/of/unittest-data/overlay_bad_unresolved.dtso

···
 /plugin/;
 
 &this_label_does_not_exist {
-	status = "ok";
+	status = "okay";
 };