BUS_DMA_NOCACHE should only be used when one needs to guarantee the
created mapping has uncached memory attributes, usually as a result of buggy
hardware. Normal use cases should pass BUS_DMA_COHERENT, to create an
appropriate mapping based on the flags passed to bus_dma_tag_create().
This should have no functional change, since the DMA tags in this driver are
created without the BUS_DMA_COHERENT flag.
Reported by: mmel