Use const pointers on parsing functions

The const-ness has to be cast away when calling mbedtls_asn1_xxx
parsing functions. This is a known flaw in the mbedtls API
(https://github.com/ARMmbed/mbedtls/issues/803).

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/include/test/psa_exercise_key.h b/tests/include/test/psa_exercise_key.h
index 1c7eefc..1613237 100644
--- a/tests/include/test/psa_exercise_key.h
+++ b/tests/include/test/psa_exercise_key.h
@@ -143,8 +143,8 @@
     psa_key_derivation_operation_t* operation,
     mbedtls_svc_key_id_t key,
     psa_algorithm_t alg,
-    unsigned char* input1, size_t input1_length,
-    unsigned char* input2, size_t input2_length,
+    const unsigned char* input1, size_t input1_length,
+    const unsigned char* input2, size_t input2_length,
     size_t capacity );
 
 /** Perform a key agreement using the given key pair against its public key
@@ -198,7 +198,7 @@
  */
 int mbedtls_test_psa_exported_key_sanity_check(
     psa_key_type_t type, size_t bits,
-    uint8_t *exported, size_t exported_length );
+    const uint8_t *exported, size_t exported_length );
 
 /** Do smoke tests on a key.
  *