Okay, we're finally at the point where ->detect has become entirely
superflous.  In sd, sr and st it does nothing but return different
values that are ignored anyway, in sg it increments a variable
that is never read (and thus removed in this patch aswell), only
in osst it increments a variable that is actually checked for beeing
non-zero.  But if it was zero we'd never reached that place anyway
(same check in the beginning of osst_detect and osst_attach).

This make the upper layer interface a lot nicer and avoids the
race condition where a device is remove between detect and attach
(which currently wouldn't matter anyway as we aren't doing anything
in detect anymore)