bnx2: fix dma_get_ops compilation breakage

This removes dma_get_ops() prefetch optimization in bnx2.

bnx2 uses dma_get_ops() to see if dma_sync_single_for_cpu() is
noop. bnx2 does prefetch if it's noop.

But dma_get_ops() isn't available on all the architectures (only the
architectures that uses dma_map_ops struct have it). Using
dma_get_ops() in drivers leads to compilation breakage on many
architectures.

This patch removes dma_get_ops() and changes bnx2 to do prefetch on
all the architectures. This adds useless prefetch on non-coherent
architectures but this is harmless. It is also unlikely to cause the
performance drop.

[ Remove now unused local variable 'pdev' -DaveM ]

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Acked-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>