net: calxeda: Fix wrong function name in comments

Fixes the following W=1 kernel build warning(s):

 drivers/net/ethernet/calxeda/xgmac.c:720: warning: expecting prototype for init_xgmac_dma_desc_rings(). Prototype was for xgmac_dma_desc_rings_init() instead
 drivers/net/ethernet/calxeda/xgmac.c:867: warning: expecting prototype for xgmac_tx(). Prototype was for xgmac_tx_complete() instead
 drivers/net/ethernet/calxeda/xgmac.c:1049: warning: expecting prototype for xgmac_release(). Prototype was for xgmac_stop() instead
 drivers/net/ethernet/calxeda/xgmac.c:1822: warning: expecting prototype for xgmac_dvr_remove(). Prototype was for xgmac_remove() instead

Signed-off-by: Yang Shen <shenyang39@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>