greybus: Remove unused field from data_connection

Audio codec driver internally maintains a struct containing info about
module's data connection. Remove unused field from this struct.

Signed-off-by: Vaibhav Agarwal <vaibhav.agarwal@linaro.org>
Reviewed-by: Mark Greer <mgreer@animalcreek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>