staging: comedi: usbduxfast: adding missing break in case statement

Added a missing "break" which forced the board to acquire 16
channels even when only 3 had been requested.
Thanks for Hartley Sweeten to spot this bug.
Signed-off-by: Bernd Porr <mail@berndporr.me.uk>
Reported-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/usbduxfast.c

@@ -745,6 +745,7 @@ static int usbduxfast_ai_cmd(struct comedi_device *dev,
 				    0x00, (0xff - 0x02) & rngmask, 0x00);
 
 		usbduxfast_cmd_data(dev, 6, 0x01, 0x00, rngmask, 0x00);
+		break;
 
 	case 16:
 		if (CR_RANGE(cmd->chanlist[0]) > 0)