staging: comedi: hwdrv_apci1564: tidy up apci1564_counter_insn_write()

Clear the gate and trig bits in the common code path.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>