amd-xgbe: Fix error return code in xgbe_probe()

Fix to return a negative error code from the setting real tx queue
count error handling case instead of 0.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>