Claude review: misc: fastrpc: Fail Audio PD init when reserved memory is missing

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**Verdict: Looks good, minor observation.**

The validation is correct and prevents NULL dereferences:

```c
+	if (!fl->cctx->remote_heap ||
+	    !fl->cctx->remote_heap->dma_addr ||
+	    !fl->cctx->remote_heap->size) {
+		err = -ENOMEM;
+		goto err;
+	}
```

Minor note: Checking `!fl->cctx->remote_heap->dma_addr` could theoretically be a false positive if a DMA address is legitimately 0, but in practice reserved-memory regions on ARM platforms will never map to physical address 0. This is a standard defensive check.

This patch is superseded by patch 4 for mainline but is important for stable backports. The error code `-ENOMEM` is reasonable since the memory region is absent.

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