sis190: Rx path update

- remove the function pointer to help gcc optimizing the
  inline pci_dma functions
- pci_dma_sync_single_for_cpu is not needed for a single
  large packet
- convert rtl8169_try_rx_copy to bool

b449655ff52ff8a29c66c5fc3fc03617e61182ee did the same
for the r8169 driver.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>