staging: comedi: amplc_pci230: Remove forward declarations 3

Move these functions and remove their forward declarations:
pci230_ao_stop(), pci230_handle_ao_nofifo(), pci230_handle_ao_fifo().
Also move pci230_ao_cancel() for aesthetic reasons.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>