net: sis: Fix a function name in comments

Use dma_alloc_coherent() instead of pci_alloc_consistent(),
because only dma_alloc_coherent() is called here.

Signed-off-by: Cai Huoqing <caihuoqing@baidu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>