staging: comedi: addi_apci_3120: reset fifo after programming chanlist

The APCI-3120 documentation says that the FIFO should be reset after the
chanlist sequence is programmed.

Reset the FIFO after programming the chanlist and remove the extra FIFO
resets in the driver.

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>