staging: comedi: adv_pci1710: transfer all ai samples in one step

The two step process to transfer the ai samples in pci1710_handle_fifo() doesn't
make any sense. If the async buffer does not have enough room for the samples the
core will set the async event COMEDI_CB_OVERFLOW which will cause the async command
to cancel. Splitting the transfer doesn't add any value.

Transfer all the samples in one step to simplify the code.

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>