bnx2: Eliminate AER error messages on systems not supporting it

On PPC for example, AER is not supported and we see unnecessary AER
error message without this patch:

bnx2 0003:01:00.1: pci_cleanup_aer_uncorrect_error_status failed 0xfffffffb

Reported-by: Breno Leitao <leitao@linux.vnet.ibm.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>