dma-buf: set signaling bit for the stub fence

Here's setting software signaling bit for the stub fence
which is always signaled. If this fence signaling bit is
not set then the AMD GPU scheduler will cause a GPU reset
due to a GPU scheduler cleanup activity timeout.

Signed-off-by: Arvind Yadav <Arvind.Yadav@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220914164321.2156-3-Arvind.Yadav@amd.com


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