USB: mos7840: remove invalid disconnect handling

commit e681b66f2e19fadbe8a7e2a17900978cb6bc921f upstream.

Remove private zombie flag used to signal disconnect and to prevent
control urb from being submitted from interrupt urb completion handler.

The control urb will not be re-submitted as both the control urb and the
interrupt urb is killed on disconnect.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>