XArray: Change xa_insert to return -EBUSY

Userspace translates EEXIST to "File exists" which isn't a very good
error message for the problem.  "Device or resource busy" is a better
indication of what went wrong.

Signed-off-by: Matthew Wilcox <willy@infradead.org>

fs/nilfs2/btnode.c

@@ -189,7 +189,7 @@ retry:
 		 */
 		if (!err)
 			return 0;
-		else if (err != -EEXIST)
+		else if (err != -EBUSY)
 			goto failed_unlock;
 
 		err = invalidate_inode_pages2_range(btnc, newkey, newkey);