[PATCH] DM: Fix bug: BIO_RW_BARRIER requests to md/raid1 hang.

Both R1BIO_Barrier and R1BIO_Returned are 4 !!!!

This means that barrier requests don't get returned (i.e.  b_endio called)
because it looks like they already have been.
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

include/linux/raid/raid1.h

@@ -130,6 +130,6 @@ struct r1bio_s {
  * with failure when last write completes (and all failed).
  * Record that bi_end_io was called with this flag...
  */
-#define	R1BIO_Returned 4
+#define	R1BIO_Returned 6
 
 #endif