In prep for the new tri-state mount option which then introduces
EXT4_MOUNT_DAX_NEVER.
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>

Link: https://lore.kernel.org/r/20200528150003.828793-4-ira.weiny@intel.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>