dma-buf: fence-chain: Document missing dma_fence_chain_init() parameter in kerneldoc

Fix W=1 compile warnings (invalid kerneldoc):

    drivers/dma-buf/dma-fence-chain.c:233: warning: Function parameter or member 'seqno' not described in 'dma_fence_chain_init'
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200819175134.19261-2-krzk@kernel.org

drivers/dma-buf/dma-fence-chain.c

@@ -222,6 +222,7 @@ EXPORT_SYMBOL(dma_fence_chain_ops);
  * @chain: the chain node to initialize
  * @prev: the previous fence
  * @fence: the current fence
+ * @seqno: the sequence number to use for the fence chain
  *
  * Initialize a new chain node and either start a new chain or add the node to
  * the existing chain of the previous fence.