test: fix max value in test_mx32

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/tests/suites/test_suite_pk.function b/tests/suites/test_suite_pk.function
index 684a90a..0591029 100644
--- a/tests/suites/test_suite_pk.function
+++ b/tests/suites/test_suite_pk.function
@@ -1131,7 +1131,7 @@
 void pk_rsa_overflow()
 {
     mbedtls_pk_context pk;
-    size_t hash_len = SIZE_MAX, sig_len = SIZE_MAX;
+    size_t hash_len = UINT_MAX + 1, sig_len = UINT_MAX + 1;
     unsigned char hash[50], sig[100];
 
     mbedtls_pk_init(&pk);