snd-aloop working no more on 1.2.7.1

[GitHub issues - edited]

alsa-project/alsa-lib issue #251 was edited from tramchamploo:

```
pcm.er4s {
    # Direct hardware access
    type        hw

    # Loopback card name
    #
    # Has to match "id" in the options of the snd-aloop module
    card        "Loopback"

    # Loopback device ID
    device      0

    # Number of audio channels
    #
    # Has to match the number of channels in music player app
    # and in the CamillaDSP input configuration
    channels    2

    # Format of audio stream
    #
    # Has to match the format defined in the
    # of the CamillaDSP input configuration
    format      "FLOAT_LE"

    # Sampling-rate of audio stream
    #
    # Has to match the sampling-rate defined in the
    # CamillaDSP configuration
    rate        48000
}


ctl.er4s {
    type hw
    card "Loopback"
}
```
This is the .asoundrc I'm using, it worked before this update.
Now aplay -L doesn't show this device.
Using mpd to play to the Loopback gets `snd_pcm_hw_params() failed: Invalid argument`.

Btw, alsa should really have a detailed specification on asoundrc file. The value of the format option I specify is from a dsp project, otherwise I have no idea what to write here. And according to [https://www.alsa-project.org/alsa-doc/alsa-lib/group___p_c_m.html#gaa14b7f26877a812acbb39811364177f8](snd_pcm_format_t) it's in a totally different format.

Issue URL     : https://github.com/alsa-project/alsa-lib/issues/251
Repository URL: https://github.com/alsa-project/alsa-lib