[PATCH] md: fix bug when raid1 attempts a partial reconstruct.

The logic here is wrong.  if fullsync is 0, it WILL BUG.

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>