qede: remove some unused code in function qede_selftest_receive_traffic

Remove set but not used variables 'sw_comp_cons' and 'hw_comp_cons'
to fix gcc '-Wunused-but-set-variable' warning:

drivers/net/ethernet/qlogic/qede/qede_ethtool.c: In function qede_selftest_receive_traffic:
drivers/net/ethernet/qlogic/qede/qede_ethtool.c:1569:20:
 warning: variable sw_comp_cons set but not used [-Wunused-but-set-variable]
drivers/net/ethernet/qlogic/qede/qede_ethtool.c: In function qede_selftest_receive_traffic:
drivers/net/ethernet/qlogic/qede/qede_ethtool.c:1569:6:
 warning: variable hw_comp_cons set but not used [-Wunused-but-set-variable]

After removing 'hw_comp_cons',the memory barrier 'rmb()' and its comments become useless,
so remove them as well.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>