md: remove sparse waring "symbol xxx shadows an earlier one"

Rename some variable and remove some duplicate definitions
to avoid there warnings.  None of them are actual errors.

Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index d0a2152..8bca383 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1773,7 +1773,7 @@
 	max_sync = RESYNC_PAGES << (PAGE_SHIFT-9);
 	if (!test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
 		/* recovery... the complicated one */
-		int i, j, k;
+		int j, k;
 		r10_bio = NULL;
 
 		for (i=0 ; i<conf->raid_disks; i++)