HID: fix up .raw_event() documentation

The documentation for the .raw_event() callback says that if the
driver return 1, there will be no further processing of the event,
but this is not true, the actual code in hid-core.c looks like this:

  if (hdrv && hdrv->raw_event && hid_match_report(hid, report)) {
           ret = hdrv->raw_event(hid, report, data, size);
           if (ret < 0)
                   goto unlock;
   }

   ret = hid_report_raw_event(hid, type, data, size, interrupt);

The only return value that has any effect on the processing is
a negative error.

Correct this as it seems to confuse people: I found bogus code in
the Razer out-of-tree driver attempting to return 1 here.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>