fix(tc): Correct return type

The fact that this was void instead of int, as required, caused
the test-running code to assume that the tests always failed.

Fixing the return type fixes the always-tests-failing bug.

Signed-off-by: Jimmy Brisson <jimmy.brisson@arm.com>
Change-Id: Ief55fe15c437c87dac1d03419a8e148f5d864b8d

plat/arm/board/tc/rss_ap_tests.c

@@ -56,7 +56,7 @@ static int run_tests(void)
 	return 0;
 }
 
-void run_platform_tests(void)
+int run_platform_tests(void)
 {
 	size_t i;
 	int ret;