Only poison memory when buffer copying is enabled

Make sure that we don't enable memory poisoning when
MBEDTLS_PSA_COPY_CALLER_BUFFERS is disabled.

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/tests/include/test/psa_crypto_helpers.h b/tests/include/test/psa_crypto_helpers.h
index 55f24e0..18d46d8 100644
--- a/tests/include/test/psa_crypto_helpers.h
+++ b/tests/include/test/psa_crypto_helpers.h
@@ -21,7 +21,8 @@
 #include "mbedtls/psa_util.h"
 #endif
 
-#if defined(MBEDTLS_TEST_HOOKS) && defined(MBEDTLS_PSA_CRYPTO_C)
+#if defined(MBEDTLS_TEST_HOOKS) && defined(MBEDTLS_PSA_CRYPTO_C) \
+    && defined(MBEDTLS_PSA_COPY_CALLER_BUFFERS)
 #include "test/psa_memory_poisoning_wrappers.h"
 #endif