xfs: return corresponding errcode if xfs_initialize_perag() fail

In xfs_initialize_perag(), if kmem_zalloc(), xfs_buf_hash_init(), or
radix_tree_preload() failed, the returned value 'error' is not set
accordingly.

Reported-as-fixing: 8b26c582 ("xfs: handle ENOMEM correctly during initialisation of perag structures")
Fixes: 9b247179 ("xfs: cache unlinked pointers in an rhashtable")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>