drm/i915/guc: Rename client->cookie to match use

The client->cookie is a shadow of the doorbell->cookie value, so rename
it to indicate its association with the doorbell, like the doorbell id
and offset.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161129121024.22650-3-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_uc.h

@@ -74,7 +74,7 @@ struct i915_guc_client {
 	uint32_t proc_desc_offset;
 
 	uint32_t doorbell_offset;
-	uint32_t cookie;
+	uint32_t doorbell_cookie;
 	uint16_t doorbell_id;
 	uint16_t padding[3];		/* Maintain alignment		*/