bnx2: Handle DMA mapping errors.

Before, the driver would not care about the return codes from pci_map_*
functions.  This could be potentially dangerous if a mapping failed.
Now, we will check all pci_map_* calls.  On the transmit side, we switch
to use the new function skb_dma_map().  On the receive side, we add
pci_dma_mapping_error().

Signed-off-by: Benjamin Li <benli@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>