of: overlay: Call of_changeset_init() early

In the Linux kernel, the following vulnerability has been resolved: of: overlay: Call of_changeset_init() early When of_overlay_fdt_apply() fails, the changeset may be partially applied, and the caller is still expected to call of_overlay_remove() to clean up this partial state. However, of_overlay_apply() calls of_resolve_phandles() before init_overlay_changeset(). Hence if the overlay fails to apply due to an unresolved symbol, the overlay_changeset.cset.entries list is still uninitialized, and cleanup will crash with a NULL-pointer dereference in overlay_removal_is_ok(). Fix this by moving the call to of_changeset_init() from init_overlay_changeset() to of_overlay_fdt_apply(), where all other early initialization is done.