net: chelsio: cxgb2: remove unused array pci_speed

Array pci_speed is defined but is never used hence it is redundant
and can be removed.

Cleans up clang warning:
warning: 'pci_speed' defined but not used [-Wunused-const-variable=]

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>