Claude review: gpu: nova-core: vbios: simplify setup_falcon_data

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

Patch Review

Good simplification. Eliminates the mutable `offset` and `pmu_in_first_fwsec` flag by computing `pmu_lookup_data` directly in a single branch. The success path is un-nested.

**Concern:** In the `else` branch:
```rust
self.base.data.get(offset - first_fwsec.base.data.len()..)
```

This subtraction `offset - first_fwsec.base.data.len()` is unchecked. The `else` arm is entered when `offset >= first_fwsec.base.data.len()`, so this cannot underflow. However, the earlier patches in this series were specifically about hardening against firmware-derived values, and `offset` is firmware-derived. The condition `offset >= first_fwsec.base.data.len()` does guarantee no underflow, so this is technically safe, but using `checked_sub` would be more consistent with the spirit of the series. This is a minor nit since the `.get()` after the subtraction still prevents OOB reads.

Also note this `else` branch uses `self.base.data` which is the second FwSec builder's data -- this gets updated to `second_fwsec.data` in patch 10 which is fine.

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