dma-buf: fix htmldocs error for dma_buf_attach_revocable

dma-buf: fix htmldocs error for dma_buf_attach_revocable

linux-next testing showed this htmldoc error due to a missing extra
line in the comments; add it.

Fixes: be6d4c9e9d714 ("dma-buf: Add dma_buf_attach_revocable()")
Reported-by: Mark Brown <broonie@kernel.org>
Closes: https://lore.kernel.org/lkml/adaNJaF58PZlvs6K@sirena.org.uk/
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patch.msgid.link/20260410123703.937822-1-sumit.semwal@linaro.org