md/raid10: always initialise ->state on newly allocated r10_bio

Most places which allocate an r10_bio zero the ->state, some don't.
As the r10_bio comes from a mempool, and the allocation function uses
kzalloc it is often zero anyway.  But sometimes it isn't and it is
best to be safe.

I only noticed this because of the bug fixed by an earlier patch
where the r10_bios allocated for a reshape were left around to
be used by a subsequent resync.  In that case the R10BIO_IsReshape
flag caused problems.
Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/raid10.c

@@ -3082,6 +3082,7 @@ static sector_t sync_request(struct mddev *mddev, sector_t sector_nr,
 			}
 
 			r10_bio = mempool_alloc(conf->r10buf_pool, GFP_NOIO);
+			r10_bio->state = 0;
 			raise_barrier(conf, rb2 != NULL);
 			atomic_set(&r10_bio->remaining, 0);
 
@@ -3270,6 +3271,7 @@ static sector_t sync_request(struct mddev *mddev, sector_t sector_nr,
 		if (sync_blocks < max_sync)
 			max_sync = sync_blocks;
 		r10_bio = mempool_alloc(conf->r10buf_pool, GFP_NOIO);
+		r10_bio->state = 0;
 
 		r10_bio->mddev = mddev;
 		atomic_set(&r10_bio->remaining, 0);
@@ -4385,6 +4387,7 @@ static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr,
 read_more:
 	/* Now schedule reads for blocks from sector_nr to last */
 	r10_bio = mempool_alloc(conf->r10buf_pool, GFP_NOIO);
+	r10_bio->state = 0;
 	raise_barrier(conf, sectors_done != 0);
 	atomic_set(&r10_bio->remaining, 0);
 	r10_bio->mddev = mddev;