UPSTREAM: dma-buf: cleanup dma_fence_unwrap selftest v2

The selftests, fix the error handling, remove unused functions and stop
leaking memory in failed tests.

v2: fix the memory leak correctly.

Change-Id: I09e0d050979f8a19c7a1b87531ed1947e8df450e
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220518135844.3338-2-christian.koenig@amd.com


(cherry picked from commit 0c5064fa)
Bug: 394776841
Bug: 397845301
Signed-off-by: T.J. Mercier <tjmercier@google.com>