ethernet: remove redundant memset

kvzalloc already zeroes the memory during the allocation.
pci_alloc_consistent calls dma_alloc_coherent directly.
In commit 518a2f19
("dma-mapping: zero memory returned from dma_alloc_*"),
dma_alloc_coherent has already zeroed the memory.
So the memset after these function is not needed.

Signed-off-by: Fuqian Huang <huangfq.daxian@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>