reiserfs: fix extended attributes on the root directory

Since commit d0a5b995 (vfs: Add IOP_XATTR inode operations flag)
extended attributes haven't worked on the root directory in reiserfs.

This is due to reiserfs conditionally setting the sb->s_xattrs handler
array depending on whether it located or create the internal privroot
directory.  It necessarily does this after the root inode is already
read in.  The IOP_XATTR flag is set during inode initialization, so
it never gets set on the root directory.

This commit unconditionally assigns sb->s_xattrs and clears IOP_XATTR on
internal inodes.  The old return values due to the conditional assignment
are handled via open_xa_root, which now returns EOPNOTSUPP as the VFS
would have done.

Link: https://lore.kernel.org/r/20191024143127.17509-1-jeffm@suse.com
CC: stable@vger.kernel.org
Fixes: d0a5b995

 ("vfs: Add IOP_XATTR inode operations flag")
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Jan Kara <jack@suse.cz>