greybus: switch cport id used for sends

In talking with Perry today I learned that the CPort id expected to
supplied over the HSIC interface to the APB is different from the
way I understood it.

My understanding was that the CPort id to supply always specified
the CPort id on the other end of a connection.  However, Perry says
the mapping between local CPort id and remote CPort id (and device
id) is done by the host UniPro interface.

So whether sending or receiving data, the CPort id that the Greybus
code should supply to the AP Bridge is the one representing the AP
side of a connection.

This patch fixes this.  The receive side already used that CPort id;
it's only the sending code that needed to be changed.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>