USB: otg: add otg_put_transceiver()

As Russell King points out, calling put_device(otg_transceiver->dev)
directly in driver cleanup paths makes assumptions about otg_transceiver
internals.

Signed-off-by: Philipp Zabel <philipp.zabel@gmail.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>