net/iavf: fix Tx threshold check

Function check_tx_thresh is called with wrong parameter. If the
check fails, tx_queue_setup should return error not keep going.
This patch fixes above issues.

Fixes: 69dd4c3d0898 ("net/avf: enable queue and device")
Cc: stable@dpdk.org
Signed-off-by: Xiaoyun Li <xiaoyun.li@intel.com>
Acked-by: Beilei Xing <beilei.xing@intel.com>