openocd: use macro ARRAY_SIZE()

There are still few cases where the macro ARRAY_SIZE() should be
used in place of custom code.

Use ARRAY_SIZE() whenever possible.

Change-Id: Iba0127a02357bc704fe639e08562a4f9aa7011df
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/6260
Reviewed-by: Xiang W <wxjstz@126.com>
Tested-by: jenkins