greybus: get rid of cport_id_map_lock

The only time we get a cport id is when setting up a new connection.
We already have a (coarser-grained) spin lock that's used to protect
the connection lists, and we can use that same lock for protecting
the hd's connection id map.

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