net: ethernet: stmicro: stmmac: Fix compile error when STMMAC_XMIT_DEBUG used

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c: In function:
stmmac_xmit drivers/net/ethernet/stmicro/stmmac/stmmac_main.c:1902:74:
error: expected ) before __func__

Signed-off-by: Dinh Nguyen <dinguyen@altera.com>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
CC: David S. Miller <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>