[NET]: Fix warnings in 3c523.c and ni52.c

We have to put back the cast to "char *" because these
pointers are volatile.

Reported by Andrew Morton.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/3c523.c b/drivers/net/3c523.c
index a384f7d..da1a22c 100644
--- a/drivers/net/3c523.c
+++ b/drivers/net/3c523.c
@@ -1145,7 +1145,7 @@
 
 	if (len != skb->len)
 		memset((char *) p->xmit_cbuffs[p->xmit_count], 0, ETH_ZLEN);
-	skb_copy_from_linear_data(skb, p->xmit_cbuffs[p->xmit_count], skb->len);
+	skb_copy_from_linear_data(skb, (char *) p->xmit_cbuffs[p->xmit_count], skb->len);
 
 #if (NUM_XMIT_BUFFS == 1)
 #ifdef NO_NOPCOMMANDS