block: fix an error code in add_partition()

[ Upstream commit 7bd897cfce1eb373892d35d7f73201b0f9b221c4 ]

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>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>