[BUGs] must check return value of pci_map_single()/pci_map_page()

Hi all,

According to Documentation/DMA-mapping.txt one should
check the return value of pci_map_single()/pci_map_page()
using pci_dma_mapping_error(), but many drivers do not.
(I have checked in drivers/net/* for example).

Should we add __must_check in the definitions/declarations 
of these functions/macros "to force" the check?

Best regards

Marin Mitov