MPC512X: Cleanup bus clock names.

Signed-off-by: Grzegorz Bernacki <gjb@semihalf.com>
diff --git a/cpu/mpc512x/fec.c b/cpu/mpc512x/fec.c
index 675b7a2..c226a8a 100644
--- a/cpu/mpc512x/fec.c
+++ b/cpu/mpc512x/fec.c
@@ -299,7 +299,7 @@
 		 * Set MII_SPEED = (1/(mii_speed * 2)) * System Clock
 		 * and do not drop the Preamble.
 		 */
-		fec->eth->mii_speed = (((gd->ipb_clk / 1000000) / 5) + 1) << 1;
+		fec->eth->mii_speed = (((gd->ips_clk / 1000000) / 5) + 1) << 1;
 
 		/*
 		 * Reset PHY, then delay 300ns