Don't initialize force-feedback for devices that don't support it to avoid calls
to schedule_work() with an uninitialized work_struct.

Move the cancel_work_sync() call out of sony_destroy_ff() since the state worker
is used for the LEDs even when force-feedback is disabled.

Remove sony_destroy_ff() to avoid a compiler warning since it is no longer used.
Signed-off-by: Frank Praznik <frank.praznik@oh.rr.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>