md: fix clearing of 'blocked' flag in the presence of bad blocks.

When the 'blocked' flag on a device is cleared while there are
unacknowledged bad blocks we must fail the device.  This is needed for
backwards compatability of the interface.

The code currently uses the wrong test for "unacknowledged bad blocks
exist".  Change it to the right test.

Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/md.c b/drivers/md/md.c
index aca6117..3742ce8 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -2592,7 +2592,7 @@
 		err = 0;
 	} else if (cmd_match(buf, "-blocked")) {
 		if (!test_bit(Faulty, &rdev->flags) &&
-		    test_bit(BlockedBadBlocks, &rdev->flags)) {
+		    rdev->badblocks.unacked_exist) {
 			/* metadata handler doesn't understand badblocks,
 			 * so we need to fail the device
 			 */