use the wrong API when free dma. So when map dma use a flag to
demostrate whether it is 'pci_map_single' or 'pci_map_page'. When free
the dma, check the flags to select the right APIs('pci_unmap_single'
or 'pci_unmap_page').

set the flags type to u16  instead of unsigned long  on David's comments.
Signed-off-by: Jie Yang <jie.yang@atheros.com>
Signed-off-by: David S. Miller <davem@davemloft.net>