Documentation: md: md-cluster.txt: Fix typos

Fix typos in md-cluster.txt file to make documentation clear.
Signed-off-by: NTamara Diaconita <diaconita.tamara@gmail.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/md/md-cluster.txt

@@ -77,7 +77,7 @@ There are three groups of locks for managing the device:
  3.1.2 RESYNCING: informs other nodes that a resync is initiated or
    ended so that each node may suspend or resume the region.  Each
    RESYNCING message identifies a range of the devices that the
-   sending node is about to resync. This over-rides any pervious
+   sending node is about to resync. This overrides any previous
    notification from that node: only one ranged can be resynced at a
    time per-node.