Only initialize force feedback for devices that actually support it (Sixaxis and
Dualshock 4) to prevent calls to schedule_work() with an uninitialized work
queue.

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 the sony_destroy_ff() function since it is no longer used.
Signed-off-by: Frank Praznik <frank.praznik@oh.rr.com>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>