Impact: cleanup

Found this when I changed args to __module_param_call.  We now have
core_param for exactly this, but Greg assures me "nousb" is used as a
module parameter, so we need the #ifdef MODULE.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Pete Zaitcev <zaitcev@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>