3w-xxxx: Prevent data corruption

Use default DMA data direction to prevent data corruption
when using SWIOTLB with 4GB+ on EM64T.

http://www.3ware.com/KB/article.aspx?id=15243&cNode=6I1C6S



Acked-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Adrian Bunk <bunk@kernel.org>