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/post.c b/post/post.c
index ecea1e1..7660224 100644
--- a/post/post.c
+++ b/post/post.c
@@ -196,7 +196,7 @@
 			 POST_CRITICAL };
 	char *var[] = { "post_poweron", "post_normal", "post_slowtest",
 			"post_critical" };
-	int varnum = sizeof (var) / sizeof (var[0]);
+	int varnum = ARRAY_SIZE(var);
 	char list[128];			/* long enough for POST list */
 	char *name;
 	char *s;