ext4: handle dax mount option collision

Mount options dax=inode and dax=never collided with fast_commit and
journal checksum. Redefine the mount flags to remove the collision.

Reported-by: Murphy Zhou <jencce.kernel@gmail.com>
Fixes: 9cb20f94 ("fs/ext4: Make DAX mount option a tri-state")
Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/20201111183209.447175-1-harshads@google.com


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