rrunner: use offsetof() instead of homegrown insanity

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/drivers/net/rrunner.h b/drivers/net/rrunner.h
index 6a79825..6173f11 100644
--- a/drivers/net/rrunner.h
+++ b/drivers/net/rrunner.h
@@ -838,7 +838,7 @@
 				   unsigned long offset,
 				   unsigned char *buf,
 				   unsigned long length);
-static u32 rr_read_eeprom_word(struct rr_private *rrpriv, void * offset);
+static u32 rr_read_eeprom_word(struct rr_private *rrpriv, size_t offset);
 static int rr_load_firmware(struct net_device *dev);
 static inline void rr_raz_tx(struct rr_private *, struct net_device *);
 static inline void rr_raz_rx(struct rr_private *, struct net_device *);