usb: typec: ucsi: displayport: Fix a potential race during registration

commit 081da132 upstream.

Locking the connector in ucsi_register_displayport() to make
sure that nothing can access the displayport alternate mode
before the function has finished and the alternate mode is
actually ready.

Fixes: af8622f6

 ("usb: typec: ucsi: Support for DisplayPort alt mode")
Cc: stable@vger.kernel.org
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20200311130006.41288-3-heikki.krogerus@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>