tests/test_seq.c: Avoid duplicate definition of ARRAY_SIZE

Avoid duplicate definition of "ARRAY_SIZE" macro in environments
that already define the macro

Signed-off-by: Younghyun Park <younghyunpark@google.com>
Change-Id: I8fa5ddd0d0279cbcda160fcb232c9c481594b0f0
diff --git a/tests/test_seq.c b/tests/test_seq.c
index e5a8954..e128457 100644
--- a/tests/test_seq.c
+++ b/tests/test_seq.c
@@ -9,7 +9,9 @@
 #include "libmctp.h"
 #include "test-utils.h"
 
+#ifndef ARRAY_SIZE
 #define ARRAY_SIZE(a) (sizeof(a) / sizeof(a[0]))
+#endif
 
 struct test_ctx {
 	struct mctp			*mctp;