dma_alloc_coherent() ignores the zone specifiers so this is pointless and
confusing.

Link: https://lore.kernel.org/r/20211214163605.416288-1-hch@lst.deReviewed-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>