Most drivers should *NOT* be using these primitives; they don't need
to use this type of memory (dma-coherent), and memory returned from
kmalloc() will work just fine.
This driver handle only very low bandwith transfers. It is not an
obvious candidate for usb_alloc_coherent().
Using these calls only serves to complicate the code for no gain,
as has been shown by multiple bugs related to this allocation path.