staging: comedi: comedi_subdevice 'io_bits' should be an unsigned int

The 'io_bits' variable in the comedi_subdevice struct is a bitmask of
the input/output configuration of the the subdevice. It should be an
unsigned int to correctly represent this.

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