fs: export empty_aops

With the ->sync_page() hook gone, we have a few users that
add their own static address_space_operations without any
functions defined.

fs/inode.c already has an empty_aops that it uses for init
purposes. Lets export that and use it in the places where
an otherwise empty aops was defined.

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/fs/inode.c b/fs/inode.c
index 5f4e11a..33c963d 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -125,6 +125,14 @@
 static DECLARE_RWSEM(iprune_sem);
 
 /*
+ * Empty aops. Can be used for the cases where the user does not
+ * define any of the address_space operations.
+ */
+const struct address_space_operations empty_aops = {
+};
+EXPORT_SYMBOL(empty_aops);
+
+/*
  * Statistics gathering..
  */
 struct inodes_stat_t inodes_stat;
@@ -176,7 +184,6 @@
  */
 int inode_init_always(struct super_block *sb, struct inode *inode)
 {
-	static const struct address_space_operations empty_aops;
 	static const struct inode_operations empty_iops;
 	static const struct file_operations empty_fops;
 	struct address_space *const mapping = &inode->i_data;