drm/virtio: fix dma_fence refcount leak on error in virtio_gpu_dma_fence_wait()

drm/virtio: fix dma_fence refcount leak on error in virtio_gpu_dma_fence_wait()

dma_fence_unwrap_for_each() internally calls dma_fence_unwrap_first()
which does cursor->chain = dma_fence_get(head), taking an extra
reference. On normal loop completion, dma_fence_unwrap_next()
releases this via dma_fence_chain_walk() -> dma_fence_put().

When virtio_gpu_do_fence_wait() fails and the function returns early
from inside the loop, the cursor->chain reference is never released.
This is the only caller in the entire kernel that does an early return
inside dma_fence_unwrap_for_each.

Add dma_fence_put(itr.chain) before the early return.

Cc: stable@vger.kernel.org
Fixes: eba57fb5498f ("drm/virtio: Wait for each dma-fence of in-fence array individually")
Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://patch.msgid.link/20260607090303.92423-1-vulab@iscas.ac.cn