squashfs: constify xattr handlers

Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
diff --git a/fs/squashfs/squashfs.h b/fs/squashfs/squashfs.h
index 305ce15..733a17c 100644
--- a/fs/squashfs/squashfs.h
+++ b/fs/squashfs/squashfs.h
@@ -100,7 +100,7 @@
 extern const struct inode_operations squashfs_symlink_inode_ops;
 
 /* xattr.c */
-extern struct xattr_handler *squashfs_xattr_handlers[];
+extern const struct xattr_handler *squashfs_xattr_handlers[];
 
 /* zlib_wrapper.c */
 extern const struct squashfs_decompressor squashfs_zlib_comp_ops;