clocksource: sh_cmt: Remove nested spinlock fix

There are control flow that sh_cmt_set_next() does double
spin-lock. The callers sh_cmt_{start,stop}() already have
lock. But another callers sh_cmt_clock_event_{start,next}()
does not.

Now sh_cmt_set_next() does not lock by itself. All the
callers should hold spin-lock before calling it.

[damm@opensource.se: use __sh_cmt_set_next() to simplify code]
[damm@opensource.se: added stable, suitable for v2.6.35 + v2.6.36]
Cc: stable@kernel.org
Signed-off-by: Takashi YOSHII <takashi.yoshii.zj@renesas.com>
Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>