refactor(storage-proofs): include function in criterion_group

The function `pedersen_md_circuit_benchmark` is defined but not used,
it appears that this function should be added to the `criterion_group`
marcro call.

Found by clippy.

storage-proofs/core/benches/pedersen.rs

@@ -212,5 +212,6 @@ criterion_group!(
     pedersen_benchmark,
     pedersen_md_benchmark,
     pedersen_circuit_benchmark,
+    pedersen_md_circuit_benchmark,
 );
 criterion_main!(benches);