It turns out that this is useful on hornet and wasp SoCs but it isn't
enabled in ye olde HAL /unless/ you were using a version from one of the
business units building USB targetted devices. It eventually got fixed
for all of them as people started wanting to use the USB ports on their
SoCs (eg for flash storage, bluetooth, 4G/LTE widgets, etc.)
This is actually a fix from ath9k but I'm merging it with the available-but-
disabled code in the QCA reference HAL.
Tested:
* AR9331 SoC
f0949f0cc6