dm raid: use proper md_ro_state enumerators

dm raid: use proper md_ro_state enumerators

The dm-raid code was using hardcoded integer values to represent the
read-only/read-write state of RAID arrays instead of the proper
enumeration constants defined in the md_ro_state enumerator type.

Changes:

- Replace hardcoded integers with the appropriate md_ro_state enumerator
  values

- Add the missing MD_RDONLY setting in the post_suspend function
  (no failures have been attributed to this inconsistency, the fix
  ensures correct state transitions for completeness)

This improves code clarity and maintainability by using the defined
enumeration constants rather than magic numbers, ensuring the code
properly conforms to the established API interface.

Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>