cmocka: Surround include info with code endcode

Doxygen makes list of includes hard to read when
it is not explicitly marked as code. Surround it
with code marks to improve readability.

Signed-off-by: Krzysztof Opasiak <k.opasiak@samsung.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
diff --git a/include/cmocka.h b/include/cmocka.h
index 2980055..154b2a6 100644
--- a/include/cmocka.h
+++ b/include/cmocka.h
@@ -40,10 +40,11 @@
  *
  * These headers or their equivalents should be included prior to including
  * this header file.
- *
+ * @code
  * #include <stdarg.h>
  * #include <stddef.h>
  * #include <setjmp.h>
+ * @endcode
  *
  * This allows test applications to use custom definitions of C standard
  * library functions and types.