fs/ext4: Narrow scope of DAX check in setflags

When preventing DAX and journaling on an inode.  Use the effective DAX
check rather than the mount option.

This will be required to support per inode DAX flags.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Link: https://lore.kernel.org/r/20200528150003.828793-2-ira.weiny@intel.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>