post: use ARRAY_SIZE

We've got a handy dandy macro already for calculating the number of
elements in an array, so use it.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/post/board/lwmon/sysmon.c b/post/board/lwmon/sysmon.c
index fc828b2..72224c6 100644
--- a/post/board/lwmon/sysmon.c
+++ b/post/board/lwmon/sysmon.c
@@ -133,7 +133,7 @@
     {"+ 5 V standby", "V", &sysmon_pic, NULL, NULL,
      100, 1000, 0, 6040, 0xFF, 0xC8, 0xDE, 0, 0xC8, 0xDE, 0, 0x7C},
 };
-static int sysmon_table_size = sizeof(sysmon_table) / sizeof(sysmon_table[0]);
+static int sysmon_table_size = ARRAY_SIZE(sysmon_table);
 
 static int conversion_done = 0;