multi: fix non-constant input of fmt.Errorf

Fixed multiple cases in which a non-constact string variable was used as a
format string for fmt.Errorf.

zpay32/bech32.go

@@ -76,7 +76,8 @@ func decodeBech32(bech string) (string, []byte, error) {
 			moreInfo = fmt.Sprintf("Expected %v, got %v.",
 				expected, checksum)
 		}
-		return "", nil, fmt.Errorf("checksum failed. " + moreInfo)
+
+		return "", nil, fmt.Errorf("checksum failed. %s", moreInfo)
 	}
 
 	// We exclude the last 6 bytes, which is the checksum.