[PATCH] s390: enable write barriers in the dasd driver

The DASD device driver never reorders the I/O requests and relies on the
hardware to write all data to nonvolatile storage before signaling a
successful write.  Hence, the only thing we have to do to support write
barriers is to set the queue ordered flag.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>