staging: comedi: ii_pci20kc: fix usage of uninit scalar in ii20k_attach()

This driver supports the PCI-20001C-1a and PCI-20001C-2a carrier boards.
The -2a version has 32 on-board DIO channels. In case this variant is
detected, local variable 'has_dio' is set accordingly. Otherwise it is
left uninitialized and the following subdevice instantiation depends on
the stack. Detected by Coverity - CID 1077830.

Signed-off-by: Christian Engelmayer <cengelma@gmx.at>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>