msm: acpuclock-krait: NULL terminate L2 table for find_cur_l2_level()

find_cur_l2_level() assumes that the L2 table is NULL terminated
when it has never been terminated. Therefore, if the rate that is
read from the hardware during boot is not found in the table we
will run off the end of the table and read potential junk values.
NULL terminate all the L2 tables so that the loop in
find_cur_l2_level() is guaranteed to terminate.

Change-Id: Ia5d0213000b44def35e388fd3cadf0293344257b
Reported-by: Laura Abbot <lauraa@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>