drm/prime: use dma_buf_fd_install() to preserve export tracing

drm_gem_prime_handle_to_fd() open-codes fd reservation and install
using get_unused_fd_flags() + fd_install() directly.  This bypasses
the DMA_BUF_TRACE() call that dma_buf_fd() emits, so observability
tools relying on the trace_dma_buf_fd tracepoint silently miss all
DRM PRIME exports.

Replace the bare fd_install() with dma_buf_fd_install(), which wraps
fd_install() together with DMA_BUF_TRACE(), restoring full tracepoint
coverage.  No functional change; the fd lifecycle (get_unused_fd_flags
→ work → install) is already correct.

Note: this patch depends on dma_buf_fd_install() introduced in
"dma-buf: dma-heap: don't publish fd before copy_to_user() succeeds"
[1].

[1] https://lore.kernel.org/dri-devel/20260714114654.3885457-2-shoubaineng@gmail.com/

Suggested-by: Christian König <christian.koenig@amd.com>
Acked-by: Sumit Semwal <sumit.semwal@linaro.org>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Baineng Shou <shoubaineng@gmail.com>
Link: https://lore.kernel.org/r/20260817050457.1005285-4-shoubaineng@gmail.com
Signed-off-by: Christian König <christian.koenig@amd.com>

drivers/gpu/drm/drm_prime.c

@@ -524,7 +524,7 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev,
 		return PTR_ERR(dmabuf);
 	}
 
-	fd_install(fd, dmabuf->file);
+	dma_buf_fd_install(dmabuf, fd);
 	*prime_fd = fd;
 	return 0;
 }