staging: comedi: addi_apci_1516: remove setting of s->io_bits

This value only has meaning for dio subdevices. Don't bother setting
it for the di and do subdevices in this driver.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>