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>
diff --git a/tests/src/random.c b/tests/src/random.c
index 5ca333a..d20103c 100644
--- a/tests/src/random.c
+++ b/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,