Staging: comedi: adv_pci1710: Correct AI scan count and channel checks

For AI commands, the internal channel list used to check incoming
data was only set up partially if the channel list contained
repeats.  Set it up fully.  Also the current scan position was not
updated properly when moving a block of data from the FIFO unless
a whole number of scans was moved.

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