MPC8xx FEC driver: fix compiler warning.

Signed-off-by: Wolfgang Denk <wd@denx.de>

cpu/mpc8xx/fec.c

diff --git a/cpu/mpc8xx/fec.c b/cpu/mpc8xx/fec.c
index 5a31413..37eb481 100644
--- a/cpu/mpc8xx/fec.c
+++ b/cpu/mpc8xx/fec.c
@@ -143,7 +143,9 @@
 static int fec_recv(struct eth_device* dev);
 static int fec_init(struct eth_device* dev, bd_t * bd);
 static void fec_halt(struct eth_device* dev);
+#if defined(CONFIG_MII) || defined(CONFIG_CMD_MII)
 static void __mii_init(void);
+#endif
 
 int fec_initialize(bd_t *bis)
 {