Use static empty variable s_cputlb_empty_entry to clear entries,
also reset addend member when clearing entries.
This helps running with valgrind/memcheck

Signed-off-by:  <igor.v.kovalenko@gmail.com>

--
Kind regards,
Igor V. Kovalenko
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>