md/r5cache: fix set_syndrome_sources() for data in cache

Before this patch, device InJournal will be included in prexor
(SYNDROME_SRC_WANT_DRAIN) but not in reconstruct (SYNDROME_SRC_WRITTEN). So it
will break parity calculation. With srctype == SYNDROME_SRC_WRITTEN, we need
include both dev with non-null ->written and dev with R5_InJournal. This fixes
logic in 1e6d690b(md/r5cache: caching phase of r5cache)

Cc: stable@vger.kernel.org (v4.10+)
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Shaohua Li <shli@fb.com>

drivers/md/raid5.c

@@ -1401,7 +1401,8 @@ static int set_syndrome_sources(struct page **srcs,
 		     (test_bit(R5_Wantdrain, &dev->flags) ||
 		      test_bit(R5_InJournal, &dev->flags))) ||
 		    (srctype == SYNDROME_SRC_WRITTEN &&
-		     dev->written)) {
+		     (dev->written ||
+		      test_bit(R5_InJournal, &dev->flags)))) {
 			if (test_bit(R5_InJournal, &dev->flags))
 				srcs[slot] = sh->dev[i].orig_page;
 			else