ATHEROS-ALX: Use dma_set_mask_and_coherent and fix a bug

1. For the 64 bits dma mask use dma_set_mask_and_coherent instead of
   dma_set_mask and dma_set_coherent_mask.

2. For the 32 bits dma mask dma_set_coherent_mask is only called if
   dma_set_mask fails, which is unusual. Assuming this as a bug, fixes
   it by replacing calls to dma_set_mask and dma_set_coherent_mask by a
   call to dma_set_mask_and_coherent.

Signed-off-by: Peter Senna Tschudin <peter.senna@gmail.com>
Tested-by: Jonas Hahnfeld <hahnjo@hahnjo.de>
Signed-off-by: David S. Miller <davem@davemloft.net>