Revert "skge: check for PCI dma mapping errors"

As reported by several people...

The code in rx_clean was panic'ing so revert
commit d0249e44

.
Will redo DMA mapping checks as new patches for a later release.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>