fs/aio.c: eliminate redundant loads in put_aio_ring_file

Using a local variable we can prevent gcc from reloading
aio_ring_file->f_inode->i_mapping twice, eliminating 2x2 dependent
loads.
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/aio.c

@@ -274,14 +274,17 @@ __initcall(aio_setup);
 static void put_aio_ring_file(struct kioctx *ctx)
 {
 	struct file *aio_ring_file = ctx->aio_ring_file;
+	struct address_space *i_mapping;
+
 	if (aio_ring_file) {
 		truncate_setsize(aio_ring_file->f_inode, 0);
 
 		/* Prevent further access to the kioctx from migratepages */
-		spin_lock(&aio_ring_file->f_inode->i_mapping->private_lock);
-		aio_ring_file->f_inode->i_mapping->private_data = NULL;
+		i_mapping = aio_ring_file->f_inode->i_mapping;
+		spin_lock(&i_mapping->private_lock);
+		i_mapping->private_data = NULL;
 		ctx->aio_ring_file = NULL;
-		spin_unlock(&aio_ring_file->f_inode->i_mapping->private_lock);
+		spin_unlock(&i_mapping->private_lock);
 
 		fput(aio_ring_file);
 	}