Define ubifs_listxattr and ubifs_xattr_handlers to NULL
when CONFIG_UBIFS_FS_XATTR is not enabled, then we can
remove many ugly ifdef macros in the code.
Signed-off-by: NChengguang Xu <cgxu519@mykernel.net>
Signed-off-by: NRichard Weinberger <richard@nod.at>