staging: comedi: remove in_request_module

The `in_request_module` member of `struct comedi_device` is only ever
set to `false`, so remove the code that checks for it being `true` and
remove the member.

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