[Bug] Audio on Planck since last breaking changes 2020/02

Describe the Bug

Hi folks,

Since the breaking changes "2020 Feb 29", the Audio features on the Planck rev6 (STM32F3 mcu) are kinda messed up, the notes plays waaay too fast. I've been testing on two Plancks, either with my personal and default keymap.

In my journey trying to understand why, I learned some interesting things on the audio features of QMK by reading the sources, especially the undocumented parts like tempo/timbre. I was able to get a correct playing speed back by setting my tempo to ~200 (instead of the default value of 100), but the pitch (or timbre I guess) is still not right, at least not the same as before. set_timbre() makes no difference.

I think it comes from the numerous Chibios changes brought to QMK withthe last breaking changes, but unfortunately I don't have enough knowledge on such low-level MCU programming to investigate any further (almost 16 months of commits on Chibios, gosh that's at lot of changes ! ^^') If I checkout before the merge of PR #8064 to build my firmware, it works fine.

System Information

• Keyboard: Planck
  • Revision (if applicable): rev. 6
• Operating system: Manjaro 19.0.2 Kyria
• AVR GCC version: 5.4.0 (Docker build)

• ARM GCC version: 6.3.1 (Docker bulid)

• QMK Firmware version: 0.8.120

• Any keyboard related software installed?
  • None