DMA-API: net: octeon: use dma_coerce_mask_and_coherent()

The code sequence:
	pdev->dev.coherent_dma_mask = DMA_BIT_MASK(64);
	pdev->dev.dma_mask = &pdev->dev.coherent_dma_mask;
bypasses the architectures check on the DMA mask.  It can be replaced
with dma_coerce_mask_and_coherent(), avoiding the direct initialization
of this mask.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>