net: samsung: sxgbe: Fix wrong function name in comments

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

 drivers/net/ethernet/samsung/sxgbe/sxgbe_main.c:797: warning: expecting prototype for sxgbe_tx_clean(). Prototype was for sxgbe_tx_all_clean() instead
 drivers/net/ethernet/samsung/sxgbe/sxgbe_main.c:1026: warning: expecting prototype for sxgbe_init_tx_coalesce(). Prototype was for sxgbe_tx_init_coalesce() instead

Cc: Byungho An <bh74.an@samsung.com>
Signed-off-by: Yang Shen <shenyang39@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>