scsi: dma-mapping: always provide dma_get_cache_alignment

scsi: dma-mapping: always provide dma_get_cache_alignment

commit 860dd4424f344400b491b212ee4acb3a358ba9d9 upstream.

Provide the dummy version of dma_get_cache_alignment that always returns
1 even if CONFIG_HAS_DMA is not set, so that drivers and subsystems can
use it without ifdefs.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
[bwh: Backported to 3.2: Also delete the conflicting declaration in
 <asm-generic/dma-mapping-broken.h>]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>