swiotlb: fix kernel-doc description for swiotlb_del_transient

Describe the pool argument in the kernel-doc comment for
swiotlb_del_transient.
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

kernel/dma/swiotlb.c

@@ -1500,6 +1500,7 @@ static void swiotlb_release_slots(struct device *dev, phys_addr_t tlb_addr,
  * swiotlb_del_transient() - delete a transient memory pool
  * @dev:	Device which mapped the buffer.
  * @tlb_addr:	Physical address within a bounce buffer.
+ * @pool:       Pointer to the transient memory pool to be checked and deleted.
  *
  * Check whether the address belongs to a transient SWIOTLB memory pool.
  * If yes, then delete the pool.