net: pasemi: set a 64-bit DMA mask on the DMA device

The pasemi driver never set a DMA mask, and given that the powerpc
DMA mapping routines never check it this worked ok so far.  But the
generic dma-direct code which I plan to switch on for powerpc checks
the DMA mask and fails unsupported mapping requests, so we need to
make sure the proper 64-bit mask is set.

Reported-by: Christian Zigotzky <chzigotzky@xenosoft.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Christian Zigotzky <chzigotzky@xenosoft.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>