logfs: Free areas before calling generic_shutdown_super()

Or hit an assertion in map_invalidatepage() instead.

Signed-off-by: Joern Engel <joern@logfs.org>
diff --git a/fs/logfs/logfs.h b/fs/logfs/logfs.h
index 0dec298..59ed32c 100644
--- a/fs/logfs/logfs.h
+++ b/fs/logfs/logfs.h
@@ -596,6 +596,7 @@
 void logfs_sync_area(struct logfs_area *area);
 void logfs_sync_segments(struct super_block *sb);
 void freeseg(struct super_block *sb, u32 segno);
+void free_areas(struct super_block *sb);
 
 /* area handling */
 int logfs_init_areas(struct super_block *sb);