shmem: Convert shmem_confirm_swap to XArray

xa_load has its own RCU locking, so we can eliminate it here.
Signed-off-by: NMatthew Wilcox <willy@infradead.org>

mm/shmem.c

@@ -349,12 +349,7 @@ static int shmem_replace_entry(struct address_space *mapping,
 static bool shmem_confirm_swap(struct address_space *mapping,
 			       pgoff_t index, swp_entry_t swap)
 {
-	void *item;
-
-	rcu_read_lock();
-	item = radix_tree_lookup(&mapping->i_pages, index);
-	rcu_read_unlock();
-	return item == swp_to_radix_entry(swap);
+	return xa_load(&mapping->i_pages, index) == swp_to_radix_entry(swap);
 }
 
 /*