examples-features/ctap: Ensure the stack is created

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
diff --git a/examples-features/ctap.rs b/examples-features/ctap.rs
index 3a66eff..6ca0611 100644
--- a/examples-features/ctap.rs
+++ b/examples-features/ctap.rs
@@ -30,6 +30,8 @@
 use p256::{Scalar, SecretKey};
 use subtle::{Choice, ConditionallySelectable};
 
+libtock_core::stack_size! {0x4000}
+
 #[derive(Debug, Clone, PartialEq, Eq, Copy)]
 pub struct PrivateKey(Scalar);