[zerocopy] Update clippy lint name
[zerocopy] Update clippy lint name

Getting rid of a warning I noticed in my editor:

```
lint `clippy::cyclomatic_complexity` has been renamed to
`clippy::cognitive_complexity`

note: `#[warn(renamed_and_removed_lints)]` on by default
help: use the new name: `clippy::cognitive_complexity`
```

Test: no behavior change
Change-Id: Ic1738deed93f8c7e59a86247a1c335bcf2430b4f
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/387256
Reviewed-by: Joshua Liebow-Feeser <234d196e9838c6e234061de31cd689c2a331d758@google.com>
Testability-Review: Joshua Liebow-Feeser <234d196e9838c6e234061de31cd689c2a331d758@google.com>
Commit-Queue: Marc Khouri <73cb61b463d134f624d9be6fd167a312c1956ba3@google.com>

google/zerocopy,google/zerocopy