cxgb4: remove set but not used variable 'spd'

Fixes gcc '-Wunused-but-set-variable' warning:
drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c: In function 'print_port_info':
drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c:5147:14: warning:
 variable 'spd' set but not used [-Wunused-but-set-variable]

variable 'spd' is set but not used since
commit 547fd272 ("cxgb4: Warn if device doesn't have enough PCI bandwidth")

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>