Fix problem with devfs when unloading the dm module.

dm-ioctl.c: deregister the misc device, and its associated symlink
*before* removing the /dev/mapper dir.  [Alasdair Kergon]
--- diff/drivers/md/dm-ioctl.c	2003-01-16 11:14:59.000000000 +0000
+++ source/drivers/md/dm-ioctl.c	2003-01-21 09:55:37.000000000 +0000
@@ -1145,15 +1145,15 @@
 	return 0;
 
       failed:
-	dm_hash_exit();
 	misc_deregister(&_dm_misc);
+	dm_hash_exit();
 	return r;
 }
 
 void dm_interface_exit(void)
 {
-	dm_hash_exit();
-
 	if (misc_deregister(&_dm_misc) < 0)
 		DMERR("misc_deregister failed for control device");
+
+	dm_hash_exit();
 }