Fix build failure with MBEDTLS_PLATFORM_NV_SEED_ALT

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/suites/test_suite_entropy.function b/tests/suites/test_suite_entropy.function
index 9f10a90..d9ea441 100644
--- a/tests/suites/test_suite_entropy.function
+++ b/tests/suites/test_suite_entropy.function
@@ -1,6 +1,7 @@
 /* BEGIN_HEADER */
 #include "mbedtls/entropy.h"
 #include "mbedtls/entropy_poll.h"
+#include "mbedtls/md.h"
 #include "string.h"
 
 typedef enum