drm/i915: Don't ERROR for an expected intel_rcs_ctx_init() interruption

intel_rcs_ctx_init() can be interrupted by a signal (if it has to wait
upon a full ring to advance). Don't emit an error for this.

Testcase: igt/gem_concurrent_blit
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NTvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1454086145-16160-3-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -746,9 +746,9 @@ static int intel_rcs_ctx_init(struct drm_i915_gem_request *req)
 
 	ret = i915_gem_render_state_init(req);
 	if (ret)
-		DRM_ERROR("init render state: %d\n", ret);
+		return ret;
 
-	return ret;
+	return 0;
 }
 
 static int wa_add(struct drm_i915_private *dev_priv,