dma-buf: actually set signaling bit for private stub fences

In dma_fence_allocate_private_stub() set the signaling bit of the newly
allocated private stub fence rather than the signaling bit of the
shared dma_fence_stub.

Cc: <stable@vger.kernel.org> # v6.1
Fixes: c85d00d4fd ("dma-buf: set signaling bit for the stub fence")
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230126002844.339593-1-dakr@redhat.com

drivers/dma-buf/dma-fence.c

@@ -167,7 +167,7 @@ struct dma_fence *dma_fence_allocate_private_stub(void)
 		       0, 0);
 
 	set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
-		&dma_fence_stub.flags);
+		&fence->flags);
 
 	dma_fence_signal(fence);