greybus: get rid of gbuf->actual_length

greybus: get rid of gbuf->actual_length

Right now, the actual_length field of a gbuf is only ever assigned,
never used.  We now fill gbufs only with operation messages, and
they encode within them the amount of space "actually used" in a
buffer in a request-specific way.  As a result, there's no need
for the gbuf->actual_length field, so we can remove it.

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