format install for ramfs -D (try ramfs -d and run mkdir inside, for example)

Reference: /n/sources/patch/applied/ramfsdebug
Date: Thu Apr 24 12:17:23 CES 2008
Signed-off-by: paurea@gmail.com

--- /sys/src/cmd/ramfs.c	Thu Apr 24 12:17:10 2008
+++ /sys/src/cmd/ramfs.c	Thu Apr 24 12:17:07 2008
@@ -206,7 +206,7 @@
 				error("writing service file");
 		}
 	}
-
+	fmtinstall('M', dirmodefmt);
 	user = getuser();
 	notify(notifyf);
 	nram = 1;