Revert "xen/p2m: m2p_find_override: use list_for_each_entry_safe"

Revert "xen/p2m: m2p_find_override: use list_for_each_entry_safe"

This reverts commit b960d6c43a63ebd2d8518b328da3816b833ee8cc.

If we have another thread (very likely) touched the list, we
end up hitting a problem "that the next element is wrong because
we should be able to cope with that. The problem is that the
next->next pointer would be set LIST_POISON1. " (Stefano's
comment on the patch).

Reverting for now.

Suggested-by: Dan Carpenter <[email protected]>
Acked-by: Stefano Stabellini <[email protected]>
Signed-off-by: Konrad Rzeszutek Wilk <[email protected]>