drivers/net/fm/eth.c: Fix compile warning

Fix this:
eth.c: In function 'fm_eth_initialize':
eth.c:651:12: warning: assignment from incompatible pointer type

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/drivers/net/fm/eth.c b/drivers/net/fm/eth.c
index f7ed850..f34f4db 100644
--- a/drivers/net/fm/eth.c
+++ b/drivers/net/fm/eth.c
@@ -420,7 +420,7 @@
 	phy_shutdown(fm_eth->phydev);
 }
 
-static int fm_eth_send(struct eth_device *dev, volatile void *buf, int len)
+static int fm_eth_send(struct eth_device *dev, void *buf, int len)
 {
 	struct fm_eth *fm_eth;
 	struct fm_port_global_pram *pram;