staging: comedi: use centralized error clean-up in comedi_init()

Centralize the "clean-up on error" handling in `comedi_init()` using
`goto` statements.  Also change some of the explicit `-EIO` return
values to the error return values from the failing functions as there is
no good reason to use `-EIO` explicitly.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>