drivers: atm: eni: Add pci_dma_mapping_error() call

Added a pci_dma_mapping_error() call to check for mapping errors before
further using the dma handle. In case of error, control goes to a new label
where the incoming skb is freed. Unchecked dma handles were found using
Coccinelle:

@rule1@
expression e1;
identifier x;
@@

*x = pci_map_single(...);
 ... when != pci_dma_mapping_error(e1,x)

Signed-off-by: Tina Johnson <tinajohnson.1234@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>