dma-buf: cleanup kerneldoc of removed component

The seqno-fence was removed, cleanup the kerneldoc include as well.

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Sumit Semwal <sumit.semwal@linaro.org>
Fixes: 992c2381 ("dma-buf: nuke seqno-fence")
Link: https://patchwork.freedesktop.org/patch/msgid/20210901080002.5892-1-christian.koenig@amd.com