UBI: Fastmap: Prepare for variable sized fastmaps

The current code assumes that each fastmap has the same amount of PEBs.
So far this is true but will change soon.
Signed-off-by: Richard Weinberger <richard@nod.at>

drivers/mtd/ubi/fastmap.c

@@ -1385,7 +1385,7 @@ int ubi_update_fastmap(struct ubi_device *ubi)
 
 			ret = -ENOSPC;
 			goto err;
-		} else if (!tmp_e && old_fm) {
+		} else if (!tmp_e && old_fm && old_fm->e[i]) {
 			ret = erase_block(ubi, old_fm->e[i]->pnum);
 			if (ret < 0) {
 				int j;
@@ -1401,12 +1401,20 @@ int ubi_update_fastmap(struct ubi_device *ubi)
 		} else {
 			new_fm->e[i] = tmp_e;
 
-			if (old_fm)
+			if (old_fm && old_fm->e[i])
 				ubi_wl_put_fm_peb(ubi, old_fm->e[i], i,
 						  old_fm->to_be_tortured[i]);
 		}
 	}
 
+	/* Old fastmap is larger than the new one */
+	if (old_fm && new_fm->used_blocks < old_fm->used_blocks) {
+		for (i = new_fm->used_blocks; i < old_fm->used_blocks; i++) {
+			ubi_wl_put_fm_peb(ubi, old_fm->e[i], i,
+					  old_fm->to_be_tortured[i]);
+		}
+	}
+
 	spin_lock(&ubi->wl_lock);
 	tmp_e = ubi_wl_get_fm_peb(ubi, 1);
 	spin_unlock(&ubi->wl_lock);