Avoid an annoying message that can appear if devices are disconnected
in the middle of a USB scatterlist operation.

Message noted in http://bugzilla.kernel.org/show_bug.cgi?id=4373
(but the real issue there seems to be a SCSI level hang).
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>