USB: otg: Fix bug on remove path without transceiver

In the case where a gadget driver is removed while no
transceiver was found at probe time, a bug in
otg_put_transceiver() will trigger.

Provide symetric calls for otg_get_transceiver() and
otg_put_transceiver(), wherever a transceiver was found or
not.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>