testsuite: ztest: src: fix missing final else

cleanup_test() was missing final else statement in
the if else if construct. This commit adds else {}
to comply with coding guideline 15.7.

Signed-off-by: Jennifer Williams <jennifer.m.williams@intel.com>

subsys/testsuite/ztest/src/ztest.c

@@ -79,6 +79,8 @@ static int cleanup_test(struct unit_test *test)
 		PRINT("Test %s failed: Unused mock return values\n",
 		      test->name);
 		ret = TC_FAIL;
+	} else {
+		;
 	}
 
 	return ret;