ocfs2: remove handle argument to ocfs2_start_trans()

All callers either pass in NULL directly, or a local variable that is
already set to NULL.

The internals of ocfs2_start_trans() get a nice cleanup as a result.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>

fs/ocfs2/dir.c

@@ -442,7 +442,7 @@ static int ocfs2_extend_dir(struct ocfs2_super *osb,
 		credits = OCFS2_SIMPLE_DIR_EXTEND_CREDITS;
 	}
 
-	handle = ocfs2_start_trans(osb, NULL, credits);
+	handle = ocfs2_start_trans(osb, credits);
 	if (IS_ERR(handle)) {
 		status = PTR_ERR(handle);
 		handle = NULL;