vc04_services: vcsm-cma: Detach from the correct dmabuf

Commit d3292dae ("dma-buf: Make locking consistent in dma_buf_detach()")
added checking that the same dmabuf for which dma_buf_attach
was called is passed into dma_buf_detach, which flagged up
that vcsm-cma was passing in the wrong dmabuf.

Correct this so that we don't get the WARN on every dma_buf
release.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>