block: fix an error code in add_partition()

We don't set an error code on this path.  It means that we return NULL
instead of an error pointer and the caller does a NULL dereference.

Fixes: 6d1d8050 ("block, partition: add partition_meta_info to hd_struct")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/partition-generic.c

@@ -320,8 +320,10 @@ struct hd_struct *add_partition(struct gendisk *disk, int partno,
 
 	if (info) {
 		struct partition_meta_info *pinfo = alloc_part_info(disk);
-		if (!pinfo)
+		if (!pinfo) {
+			err = -ENOMEM;
 			goto out_free_stats;
+		}
 		memcpy(pinfo, info, sizeof(*info));
 		p->info = pinfo;
 	}