staging: comedi: das08: Correct AI encoding for das08jr-16-ao

commit e6391a18 upstream.

The element of `das08_boards[]` for the 'das08jr-16-ao' board has the
`ai_encoding` member set to `das08_encode12`.  It should be set to
`das08_encode16` same as the 'das08jr/16' board.  After all, this board
has 16-bit AI resolution.

The description of the A/D LSB register at offset 0 seems incorrect in
the user manual "cio-das08jr-16-ao.pdf" as it implies that the AI
resolution is only 12 bits.  The diagrams of the A/D LSB and MSB
registers show 15 data bits and a sign bit, which matches what the
software expects for the `das08_encode16` AI encoding method.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2: adjust indentation]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/das08.c

@@ -385,7 +385,7 @@ static const struct das08_board_struct das08_boards[] = {
 	 .ai = das08_ai_rinsn,
 	 .ai_nbits = 16,
 	 .ai_pg = das08_pg_none,
-	 .ai_encoding = das08_encode12,
+	 .ai_encoding = das08_encode16,
 	 .ao = das08jr_ao_winsn,
 	 .ao_nbits = 16,
 	 .di = das08jr_di_rbits,