drm/i915: Assign request ringbuf before pin

In preparation to make intel_lr_context_pin|unpin to accept
requests, assign ringbuf into request before we call the pinning.

v2: No need to unset ringbuf on error path (Chris)

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_lrc.c

@@ -633,14 +633,14 @@ int intel_logical_ring_alloc_request_extras(struct drm_i915_gem_request *request
 {
 	int ret;
 
+	request->ringbuf = request->ctx->engine[request->ring->id].ringbuf;
+
 	if (request->ctx != request->ring->default_context) {
 		ret = intel_lr_context_pin(request->ring, request->ctx);
 		if (ret)
 			return ret;
 	}
 
-	request->ringbuf = request->ctx->engine[request->ring->id].ringbuf;
-
 	return 0;
 }