md: raid10: fix use-after-free of bio

[Maik Hampel <m.hampel@gmx.de>]

In case of read errors raid10d tries to print a nice error message,
unfortunately using data from an already put bio.

Signed-off-by: Maik Hampel <m.hampel@gmx.de>

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index f730a14..ea1b3e3 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1557,7 +1557,6 @@ static void raid10d(mddev_t *mddev)
 			bio = r10_bio->devs[r10_bio->read_slot].bio;
 			r10_bio->devs[r10_bio->read_slot].bio =
 				mddev->ro ? IO_BLOCKED : NULL;
-			bio_put(bio);
 			mirror = read_balance(conf, r10_bio);
 			if (mirror == -1) {
 				printk(KERN_ALERT "raid10: %s: unrecoverable I/O"
@@ -1567,6 +1566,7 @@ static void raid10d(mddev_t *mddev)
 				raid_end_bio_io(r10_bio);
 			} else {
 				const int do_sync = bio_sync(r10_bio->master_bio);
+				bio_put(bio);
 				rdev = conf->mirrors[mirror].rdev;
 				if (printk_ratelimit())
 					printk(KERN_ERR "raid10: %s: redirecting sector %llu to"