ci: run clippy on acpi crate

Now that all warnings have been fixed for the acpi crate, run clippy
as part of CI. Once the warnings for the rest of the crates are fixed,
they can be included in the CI run.

.github/workflows/build.yml

@@ -64,3 +64,20 @@ jobs:
 
     - name: Run AML test suite
       run: cargo run --bin aml_tester -- -p tests --reset
+
+  clippy:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        submodules: 'recursive'
+    - name: Install Rust
+      uses: actions-rs/toolchain@v1
+      with:
+        toolchain: nightly
+        default: true
+        profile: minimal
+        components: clippy
+
+    - name: Run clippy
+      run: cargo clippy -p acpi