tests: Fix header inclusion

When building tests, the path of the library
directory is part of the possible paths for
the includes thus no need to construct it
manually when including headers.

Signed-off-by: Ronald Cron <ronald.cron@arm.com>

tests/src/random.c

@@ -36,7 +36,7 @@
 #include <string.h>
 
 #include <mbedtls/entropy.h>
-#include "../../library/alignment.h"
+#include <alignment.h>
 
 int mbedtls_test_rnd_std_rand(void *rng_state,
                               unsigned char *output,