ext2: Fix i_op setting for special inode

Let's always set special inode i_op to &ext2_special_inode_operations
regardless of CONFIG_EXT2_FS_XATTR setting. It makes sence to be able to
query extended inode flags (needing ->setattr and ->getattr callbacks)
even when CONFIG_EXT2_FS_XATTR is not set.

Link: https://lore.kernel.org/r/20200522044035.24190-1-cgxu519@mykernel.net
Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
Signed-off-by: Jan Kara <jack@suse.cz>