Add a dummy usage of a pointer in tests

This way clang with O1 doesn't optimize it.
Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>

tests/suites/test_suite_platform.function

@@ -126,6 +126,8 @@ void check_mbedtls_calloc_overallocation(intmax_t num, intmax_t size)
 {
     unsigned char *buf;
     buf = mbedtls_calloc((size_t) num, (size_t) size);
+    /* Dummy usage of the pointer to prevent optimizing it */
+    mbedtls_printf("calloc pointer : %p\n", buf);
     TEST_ASSERT(buf == NULL);
 
 exit: