USB: avoid error messages when a device is disconnected

This patch (as1673) reduces the amount of log spew from the hub driver
by removing a bunch of error messages in the case where the device in
question is already known to have been disconnected.  Since the
disconnect event itself appears in the log, there's no need for other
error messages.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Tested-by: Jenya Y <jy.gerstmaier@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>