net: fec: Add a fec_enet_clear_ethtool_stats() stub for CONFIG_M5272

Commit 2b30842b ("net: fec: Clear and enable MIB counters on imx51")
introduced fec_enet_clear_ethtool_stats(), but missed to add a stub
for the CONFIG_M5272=y case, causing build failure for the
m5272c3_defconfig.

Add the missing empty stub to fix the build failure.
Reported-by: NPaul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: NFabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/fec_main.c

@@ -2361,6 +2361,10 @@ static int fec_enet_get_sset_count(struct net_device *dev, int sset)
 static inline void fec_enet_update_ethtool_stats(struct net_device *dev)
 {
 }
+
+static inline void fec_enet_clear_ethtool_stats(struct net_device *dev)
+{
+}
 #endif /* !defined(CONFIG_M5272) */
 
 /* ITR clock source is enet system clock (clk_ahb).