StreamRecording::duration is wrong

[martinwork]

The second float cast is in the wrong place.
https://github.com/lancaster-university/codal-core/blob/509086cc8590465041b15493ab52b56e7071c110/source/streams/StreamRecording.cpp#L65

[martinwork]

Created PR lancaster-university/codal-core#172

With the test below... before the change

Recording length:   11098 bytes
Recording rate:     11000 Hz
Recording duration: 672 ms

After the change

Recording length:   11036 bytes
Recording rate:     11000 Hz
Recording duration: 1003 ms

test code

#include "MicroBit.h"
#include "StreamRecording.h"
#include "SerialStreamer.h"

MicroBit uBit;

int main() {
    uBit.init();

    static SplitterChannel *splitterChannel = uBit.audio.splitter->createChannel();

    splitterChannel->requestSampleRate(11000);

    static StreamRecording *recording = new StreamRecording(*splitterChannel);

    static MixerChannel *mixerChannel = uBit.audio.mixer.addChannel(*recording, recording->getSampleRate());

    static SerialStreamer *streamer = new SerialStreamer(*recording, SERIAL_STREAM_MODE_DECIMAL);

    MicroBitAudio::requestActivation();
    mixerChannel->setVolume(75.0);
    uBit.audio.mixer.setVolume(1023);

    uBit.serial.printf("Recording rate: %d\n", (int)recording->getSampleRate());
    uBit.serial.printf("Mixer rate: %d\n", (int)uBit.audio.mixer.getSampleRate());

    while (true) {
        if (uBit.buttonA.isPressed()) {
            uBit.sleep(500);

            uBit.display.print("R");
            recording->recordAsync();
            uBit.sleep(1000);
            recording->stop();
            uBit.serial.printf("Recording length:   %d bytes\n", (int) recording->length());
            uBit.serial.printf("Recording rate:     %d Hz\n", (int) recording->getSampleRate());
            uBit.serial.printf("Recording duration: %d ms\n", (int) ( 1000 * recording->duration( recording->getSampleRate())));
        } else if (uBit.buttonB.isPressed()) {
            uBit.display.print("P");
            recording->connect(*mixerChannel);
            recording->play();
        } else if (uBit.logo.isPressed()) {
            recording->connect(*streamer);
            recording->play();
        }
        uBit.display.clear();
        uBit.sleep(100);
    }
}