maple_tree: fix comment of mte_destroy_walk

The parameter name of maple tree is mt, make the comment be mt instead of
mn, and the separator between the parameter name and the description to be
: instead of -.

Link: https://lkml.kernel.org/r/20230111135348.803181-1-vernon2gm@gmail.com
Fixes: 54a611b605 ("Maple Tree: add new data structure")
Signed-off-by: Vernon Yang <vernon2gm@gmail.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/maple_tree.c

@@ -5579,8 +5579,8 @@ free_leaf:
 
 /*
  * mte_destroy_walk() - Free a tree or sub-tree.
- * @enode - the encoded maple node (maple_enode) to start
- * @mn - the tree to free - needed for node types.
+ * @enode: the encoded maple node (maple_enode) to start
+ * @mt: the tree to free - needed for node types.
  *
  * Must hold the write lock.
  */