dma-buf: Fix one use-after-free of fence

Need get the new fence when we replace the old one.

Fixes: 047a1b87 ("dma-buf & drm/amdgpu: remove dma_resv workaround")
Signed-off-by: xinhui pan <xinhui.pan@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220707080241.20060-1-xinhui.pan@amd.com


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