Claude review: gpu: host1x: Fix iommu_map_sgtable() return value check

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

Patch Review

**Status: Good**

The old code assigned `iommu_map_sgtable()` directly into `int err`, which has two problems: (1) it checked `== 0` for failure (inverted vs the new API), and (2) assigning `ssize_t` into `int` could truncate large success values into negative numbers, creating false failures. The commit message correctly identifies both issues.

The fix introduces a properly-typed `ssize_t map_err` local, checks `< 0`, and propagates the actual error instead of a hardcoded `-EINVAL`:

```c
+			ssize_t map_err;
...
+			map_err = iommu_map_sgtable(host->domain, iova_dma_addr(&host->iova, alloc),
+						    map->sgt, IOMMU_READ);
+			if (map_err < 0) {
 				__free_iova(&host->iova, alloc);
-				err = -EINVAL;
+				err = map_err;
```

The `err = map_err` assignment narrows `ssize_t` to `int`, but this is fine on the error path since negative errnos always fit in an `int`.

No issues.

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