net: fix typo in arp clean up

The clean up patch missed an &, so we end up passing an int rather than
a pointer to the sprintf function.

arp.c: In function 'ArpReceive':
arp.c:197: warning: format '%p' expects type 'void *', but argument 3 has type 'int'

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

net/arp.c

@@ -194,7 +194,7 @@ void ArpReceive(struct ethernet_hdr *et, struct ip_udp_hdr *ip, int len)
 #ifdef CONFIG_KEEP_SERVERADDR
 		if (NetServerIP == NetArpWaitPacketIP) {
 			char buf[20];
-			sprintf(buf, "%pM", arp->ar_sha);
+			sprintf(buf, "%pM", &arp->ar_sha);
 			setenv("serveraddr", buf);
 		}
 #endif