drm/ttm: test private resv obj on release/destroy

drm/ttm: test private resv obj on release/destroy

Test the fences in the private dma_resv object instead of the pointer to
a potentially shared dma_resv object.

This only matters for imported BOs with an SG table since those don't
get their dma_resv pointer replaced on release.

Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: James Zhu <James.Zhu@amd.com>
Reviewed-by: James Zhu <James.Zhu@amd.com>
Tested-by: James Zhu <James.Zhu@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250129152849.15777-1-christian.koenig@amd.com