greybus: kill gbuf->complete

greybus: kill gbuf->complete

The gbuf complete method is a callback that allows the creator of a
gbuf to know when all processing on a gbuf is done.

We now only ever allocate gbufs for use in Greybus operations, and
in that case we only ever supply gb_operation_gbuf_complete() as the
completion callback.  Furthermore, the only place gbuf->complete()
is called is in gb_operation_recv_work().

Knowing this, we can just call gb_operation_gbuf_complete() directly
from gb_operation_recv_work(), and get rid of the gbuf->complete()
method entirely.

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