CBUS: Do not BUG_ON in retu-headset in case of spurious release event

CBUS: Do not BUG_ON in retu-headset in case of spurious release event

There is a small chance that retu_headset_detect_timer can run twice
and pressed flag being zero in second run. Do nothing in that case instead
of throwing BUG_ON.

Double run can happen under very busy system assuming following scenario

1. Hook interrupt (run in softirq context, pressed flag = 1)
2. First retu_headset_enable_timer call
3. Busy system, retu raises an interrupt but cannot run hook interrupt for
   300-350 ms
4. Second hook interrupt
5. First retu_headset_detect_timer call (pressed flag = 0)
6. Second retu_headset_enable_timer
7. Second retu_headset_detect_timer
   -> pressed flag == 0 => BUG_ON

Patch also removes two debug messages since they are not needed very much
and removal cleans up code a bit.

Signed-off-by: Jarkko Nikula <jarkko.nikula@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>