Fix printf of enum

The enum is promoted to `int`, so `%d` is a correct format,
but `gcc -Wformat` complains.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index f86dd93..2925495 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -1351,7 +1351,7 @@
 {
     MBEDTLS_SSL_DEBUG_MSG(3, ("handshake state: %d (%s) -> %d (%s)",
                               ssl->state, mbedtls_ssl_states_str(ssl->state),
-                              state, mbedtls_ssl_states_str(state)));
+                              (int) state, mbedtls_ssl_states_str(state)));
     ssl->state = (int) state;
 }