dma-buf: fix dma-fence-chain out of order test

There was probably a misunderstand on how the dma-fence-chain is
supposed to work or what dma_fence_chain_find_seqno() is supposed to
return.

dma_fence_chain_find_seqno() is here to give us the fence to wait upon
for a particular point in the timeline. The timeline progresses only
when all the points prior to a given number have completed.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: dc2f7e67 ("dma-buf: Exercise dma-fence-chain under selftests")
Link: https://patchwork.freedesktop.org/patch/372960/


Signed-off-by: Christian König <christian.koenig@amd.com>