If one md array is waiting for another to finish resyncing, then it holds a
reference to the array, so the array cannot be stopped.  With this patch, we
drop the reference before waiting.
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>