qlcnic: Remove set but not used variables 'fw_mbx' and 'hdr_size'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/net/ethernet/qlogic/qlcnic/qlcnic_sriov_common.c: In function 'qlcnic_sriov_pull_bc_msg':
drivers/net/ethernet/qlogic/qlcnic/qlcnic_sriov_common.c:907:6: warning:
 variable 'fw_mbx' set but not used [-Wunused-but-set-variable]

drivers/net/ethernet/qlogic/qlcnic/qlcnic_sriov_common.c: In function 'qlcnic_sriov_issue_bc_post':
drivers/net/ethernet/qlogic/qlcnic/qlcnic_sriov_common.c:939:16: warning:
 variable 'hdr_size' set but not used [-Wunused-but-set-variable]

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>