ppc4xx: EMAC: Fix 405EZ fifo size setup in EMAC_MR1

The 405EZ only supports 512 bytes of rx-/tx-fifo EMAC sizes. But
currently 4k/2k is configured. This patch fixes this issue.

Thanks to Thomas Kindler <tkindler@lenord.de> for pointing this out.

Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/cpu/ppc4xx/4xx_enet.c b/cpu/ppc4xx/4xx_enet.c
index 5ef1005..599f5ce 100644
--- a/cpu/ppc4xx/4xx_enet.c
+++ b/cpu/ppc4xx/4xx_enet.c
@@ -975,9 +975,10 @@
 	/* set transmit enable & receive enable */
 	out_be32((void *)EMAC_M0 + hw_p->hw_addr, EMAC_M0_TXE | EMAC_M0_RXE);
 
-	/* set receive fifo to 4k and tx fifo to 2k */
 	mode_reg = in_be32((void *)EMAC_M1 + hw_p->hw_addr);
-	mode_reg |= EMAC_M1_RFS_4K | EMAC_M1_TX_FIFO_2K;
+
+	/* set rx-/tx-fifo size */
+	mode_reg = (mode_reg & ~EMAC_MR1_FIFO_MASK) | EMAC_MR1_FIFO_SIZE;
 
 	/* set speed */
 	if (speed == _1000BASET) {