net: replace dma_sync_single with dma_sync_single_for_cpu

This replaces dma_sync_single() with dma_sync_single_for_cpu() because
dma_sync_single() is an obsolete API; include/linux/dma-mapping.h says:

/* Backwards compat, remove in 2.7.x */
#define dma_sync_single		dma_sync_single_for_cpu
#define dma_sync_sg		dma_sync_sg_for_cpu

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>