[PATCH] libata.h needs dma-mapping.h

On Alpha:

include/linux/libata.h: In function `ata_pad_alloc':
include/linux/libata.h:785: warning: implicit declaration of function `dma_alloc_coherent'
include/linux/libata.h:786: warning: assignment makes pointer from integer without a cast
include/linux/libata.h: In function `ata_pad_free':
include/linux/libata.h:792: warning: implicit declaration of function `dma_free_coherent'

(I have a decouple-some-header-files cleanup in -mm, so it's causing some
fallout of this nature)

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>