logfs: destroy the reserved inodes while unmounting

We were assuming that the evict_inode() would never be called on
reserved inodes. However, (after the commit 8e22c1a4e logfs: get rid
of magical inodes) while unmounting the file system, in put_super, we
call iput() on all of the reserved inodes.

The following simple test used to cause a kernel panic on LogFS:

1. Mount a LogFS file system on /mnt

2. Create a file
   $ touch /mnt/a

3. Try to unmount the FS
   $ umount /mnt

The simple fix would be to drop the assumption and properly destroy
the reserved inodes.

Signed-off-by: Prasad Joshi <prasadjoshi.linux@gmail.com>
diff --git a/fs/logfs/segment.c b/fs/logfs/segment.c
index e28d090..038da09 100644
--- a/fs/logfs/segment.c
+++ b/fs/logfs/segment.c
@@ -886,7 +886,7 @@
 
 static void map_invalidatepage(struct page *page, unsigned long l)
 {
-	BUG();
+	return;
 }
 
 static int map_releasepage(struct page *page, gfp_t g)