md/raid1: minor bio initialisation improvements.

When performing a resync we pre-allocate some bios and repeatedly use
them.  This requires us to re-initialise them each time.
One field (bi_comp_cpu) and some flags weren't being initiaised
reliably.

Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/raid1.c

@@ -1839,7 +1839,9 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
 
 		/* take from bio_init */
 		bio->bi_next = NULL;
+		bio->bi_flags &= ~(BIO_POOL_MASK-1);
 		bio->bi_flags |= 1 << BIO_UPTODATE;
+		bio->bi_comp_cpu = -1;
 		bio->bi_rw = READ;
 		bio->bi_vcnt = 0;
 		bio->bi_idx = 0;