Abort in audio_calloc()  of ac97
Description of problem:
Section 5.10.2 of the AC97 specification (https://hands.com/~lkcl/ac97_r23.pdf)
shows the feasibility to support for rates other than 48kHZ. Specifically,
AC97_PCM_Front_DAC_Rate (reg 2Ch) should be from 8kHZ to 48kHZ.


An adversary can leverage this to crash QEMU.

A nornal 48kHZ setting is like this.

```
ac97_realize
  open_voice
    as->freq = 0xbb80 # 0xbb80=48000
    AUD_open_out
      audio_pcm_create_voice_pair_out (sw is NULL)
        audio_pcm_sw_init_out
          sw->info.freq = as->freq (in audio_pcm_init_info())
          sw->ratio = ((int64_t) sw->hw->info.freq << 32) / sw->info.freq
          samples = ((int64_t) sw->HWBUF->size << 32) / sw->ratio (in audio_pcm_sw_alloc_resources_out())
```

A non-48kHZ setting is like this. Since `as->freq` is too small, `sw->ratio` is
too large. Finally, `samples` is zero, failing the audio_calloc() in
audio_pcm_sw_alloc_resources_out().

```
nam_writew
  open_voice
    as->freq = 0x6
    AUD_open_out
      audio_pcm_sw_init_out (sw is not NULL)
        sw->info.freq = as->freq (in audio_pcm_init_info())
        sw->ratio = ((int64_t) sw->hw->info.freq << 32) / sw->info.freq
        samples = ((int64_t) sw->HWBUF->size << 32) / sw->ratio (in audio_pcm_sw_alloc_resources_out())
        audio_calloc(.., samples, ) (in audio_pcm_sw_alloc_resources_out())
```
Steps to reproduce:
1. download the prepared rootfs and the image.

    https://drive.google.com/file/d/1IfVCvn76HY-Eb4AZU7yvuyPzM3QC1q10/view?usp=sharing
    https://drive.google.com/file/d/1JN6JgvOSI5aSLIdTEFKiskKbrGWFo0BO/view?usp=sharing

2. run the following script.

``` bash
QEMU_PATH=../../../qemu-devel/build/x86_64-softmmu/qemu-system-x86_64
KERNEL_PATH=./bzImage
ROOTFS_PATH=./rootfs.ext2
$QEMU_PATH \
    -M q35 -m 1G \
    -kernel $KERNEL_PATH \
    -drive file=$ROOTFS_PATH,if=virtio,format=raw \
    -append "root=/dev/vda console=ttyS0" \
    -net nic,model=virtio -net user \
    -device ac97,audiodev=snd0 -audiodev none,id=snd0 \
    -nographic
```

3. with spawned shell (the user is root and the password is empty), run
`ac97-00`.
Additional information:
In the latest QEMU, this issue was generally fixed by 12f4abf6a245c43d8411577fd400373c85f08c6b and 0cbc8bd4694f32687bf47c6da48efa48fac35fd2 that remove abort() from the source code. Even though, I still plan to send a
patch so that the warning about the invalid freq will be gone.