drm/radeon: check the alloc_workqueue return value in radeon_crtc_init()

check the alloc_workqueue return value in radeon_crtc_init()
to avoid null-ptr-deref.

Fixes: fa7f517c ("drm/radeon: rework page flip handling v4")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_display.c

@@ -687,11 +687,16 @@ static void radeon_crtc_init(struct drm_device *dev, int index)
 	if (radeon_crtc == NULL)
 		return;
 
+	radeon_crtc->flip_queue = alloc_workqueue("radeon-crtc", WQ_HIGHPRI, 0);
+	if (!radeon_crtc->flip_queue) {
+		kfree(radeon_crtc);
+		return;
+	}
+
 	drm_crtc_init(dev, &radeon_crtc->base, &radeon_crtc_funcs);
 
 	drm_mode_crtc_set_gamma_size(&radeon_crtc->base, 256);
 	radeon_crtc->crtc_id = index;
-	radeon_crtc->flip_queue = alloc_workqueue("radeon-crtc", WQ_HIGHPRI, 0);
 	rdev->mode_info.crtcs[index] = radeon_crtc;
 
 	if (rdev->family >= CHIP_BONAIRE) {