UPSTREAM: dma-buf: actually set signaling bit for private stub fences

In dma_fence_allocate_private_stub() set the signaling bit of the newly
allocated private stub fence rather than the signaling bit of the
shared dma_fence_stub.

Bug: 379008999
Fixes: c85d00d4 ("dma-buf: set signaling bit for the stub fence")
Reviewed-by: Christian König <christian.koenig@amd.com>
Change-Id: I7b8faede38137044065257239c440a84c60ea238
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230126002844.339593-1-dakr@redhat.com


(cherry picked from commit 851a4a77)
Signed-off-by: T.J. Mercier <tjmercier@google.com>