drm/nouveau/core: fix return in error path of device probe

We want to unlock nv_devices_mutex in this error path as well.
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nvkm/engine/device/base.c

@@ -2494,7 +2494,8 @@ nvkm_device_ctor(const struct nvkm_device_func *func,
 		device->pri = ioremap(mmio_base, mmio_size);
 		if (!device->pri) {
 			nvdev_error(device, "unable to map PRI\n");
-			return -ENOMEM;
+			ret = -ENOMEM;
+			goto done;
 		}
 	}