Claude review: misc: fastrpc: Allow fastrpc_buf_free() to accept NULL

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

Patch Review

**Verdict: Clean, correct.**

This follows the standard kernel pattern (like `kfree`, `vfree`, etc.) of making free functions accept NULL:

```c
static void fastrpc_buf_free(struct fastrpc_buf *buf)
{
    if (!buf)
        return;
    // ...
}
```

The two callsite simplifications (`fastrpc_context_free` and `fastrpc_device_release`) are straightforward and correct. No functional change.

Note that this patch does **not** help with Patch 3's bugs — the issue there is calling `fastrpc_buf_free` on a non-NULL but improperly initialized `fastrpc_buf`, not passing NULL.

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Generated by Claude Code Patch Reviewer