staging: comedi: change type of auto-config context

Change the type of the context parameter passed to
`comedi_auto_config_helper()` from `void *` to `unsigned long`.  It's
currently just an internal change and all current internal usages pass
pointers in the context, but future uses of this function may pass
integer values or pointer values at the whim of a lower-level comedi
driver and the `unsigned long` type expresses this better as it is
commonly used in the Linux kernel to hold such values.

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