staging: comedi: cb_pcidas64: fix forward declararions 4

Move `disable_plx_interrupts()`, `disable_ai_interrupts()`,
`enable_ai_interrupts()`, `set_ai_fifo_segment_length()`,
`set_ai_fifo_size()`, `ai_fifo_size()`, `load_ao_dma_buffer()`, and
`load_ao_dma()`, and remove forward declarations of these functions.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>