drm/i915/guc: Use better name for helper wait function

In next patch we will introduce another way of waiting for the response
that will use RECV buffer. To avoid misleading names, rename old wait
function to reflect the fact that it is based on descriptor update.

v2: fix comment style (Michal)
v3: use more specific name (Michel)

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Michel Thierry <michel.thierry@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180326194829.58836-8-michal.wajdeczko@intel.com