netdev: convert non-obvious instances to use ARRAY_SIZE()

This will convert remaining non-obvious or naive calculations of array
sizes to use ARRAY_SIZE() macro.

Signed-off-by: Alejandro Martinez Ruiz <alex@flawedcode.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/drivers/net/cassini.c b/drivers/net/cassini.c
index 563bf5f..7df31b5 100644
--- a/drivers/net/cassini.c
+++ b/drivers/net/cassini.c
@@ -4443,7 +4443,7 @@
 	{REG_MAC_COLL_EXCESS},
 	{REG_MAC_COLL_LATE}
 };
-#define CAS_REG_LEN 	(sizeof(ethtool_register_table)/sizeof(int))
+#define CAS_REG_LEN 	ARRAY_SIZE(ethtool_register_table)
 #define CAS_MAX_REGS 	(sizeof (u32)*CAS_REG_LEN)
 
 static void cas_read_regs(struct cas *cp, u8 *ptr, int len)