greybus: gb-audio: Activate TX connection Bundle CPort ID

Currently, the audio driver activates & deactivates a predefined
CPort ID but that can vary depending on the manifest data of the
module.  Instead, use the TX connection's Bundle CPort ID which
contains the correct CPort ID.

Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Acked-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>