Relaxed clippy fixes/nits (#2661)

This PR contains just a few clippy fixes and nits, which are, however,
relaxed by workspace clippy settings here:
https://github.com/paritytech/polkadot-sdk/blob/master/Cargo.toml#L483-L506

---------

Co-authored-by: Dmitry Sinyavin <dmitry.sinyavin@parity.io>
Co-authored-by: ordian <write@reusable.software>
Co-authored-by: command-bot <>
Co-authored-by: Bastian Köcher <git@kchr.de>

substrate/frame/contracts/src/migration/v10.rs

@@ -219,7 +219,7 @@ where
 					"Failed to transfer the base deposit, reason: {:?}",
 					err
 				);
-				OldCurrency::deposit_creating(&deposit_account, min_balance);
+				let _ = OldCurrency::deposit_creating(&deposit_account, min_balance);
 				min_balance
 			});