Claude review: rust: dma: update to keyworded index projection syntax

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

Patch Review

Converts the DMA subsystem's documentation examples and the `rust_dma` sample driver to use the new syntax.

The doc examples are updated appropriately:
```rust
-/// let whole = kernel::dma_read!(alloc, [2]?);
-/// let field = kernel::dma_read!(alloc, [1]?.field);
+/// let whole = kernel::dma_read!(alloc, [try: 2]);
+/// let field = kernel::dma_read!(alloc, [panic: 1].field);
```

Nice that this also demonstrates the `panic` flavor in the docs, showing a case where the programmer knows the index is valid.

The sample driver conversion is also good -- the `check_dma` function signature change from `fn check_dma(&self) -> Result` to `fn check_dma(&self)` is a logical consequence of switching from `[try: i]` (which uses `?` and thus requires `Result` return) to `[panic: i]` (which panics directly and doesn't need error propagation). The call site is simplified accordingly:

```rust
-        assert!(self.check_dma().is_ok());
+        self.check_dma();
```

This is a good change -- the old `assert!(is_ok())` was effectively panicking on error anyway, so the `panic` variant is semantically equivalent but cleaner.

Already has Reviewed-by from Alice, Andreas, and Alexandre. No issues.

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Generated by Claude Code Patch Reviewer