Input: fix locking in memoryless force-feedback devices

Now that input core acquires dev->event_lock spinlock and disables
interrupts when propagating input events, using spin_lock_bh() in
ff-memless driver is not allowed. Actually, the timer_lock itself
is not needed anymore, we should simply use dev->event_lock
as well.

Also do a small cleanup in force-feedback core.

Reported-by: kerneloops.org
Reported-by: http://www.kerneloops.org/searchweek.php?search=ml_ff_set_gain
Reported-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

include/linux/input.h

@@ -1377,6 +1377,10 @@ extern struct class input_class;
  * methods; erase() is optional. set_gain() and set_autocenter() need
  * only be implemented if driver sets up FF_GAIN and FF_AUTOCENTER
  * bits.
+ *
+ * Note that playback(), set_gain() and set_autocenter() are called with
+ * dev->event_lock spinlock held and interrupts off and thus may not
+ * sleep.
  */
 struct ff_device {
 	int (*upload)(struct input_dev *dev, struct ff_effect *effect,