staging: comedi: ni_mio_common: ack ai fifo error interrupts.

Ack ai fifo error interrupts in interrupt handler to clear interrupt
after fifo overflow.  It should prevent lock-ups after the ai fifo
overflows.

Cc: <stable@vger.kernel.org> # v4.2+
Signed-off-by: Frank Mori Hess <fmh6jj@gmail.com>
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>