ibmveth: Fix DMA unmap error

ibmveth: Fix DMA unmap error

commit 33a48ab105a75d37021e422a0a3283241099b142 upstream.

Commit 6e8ab30ec677 (ibmveth: Add scatter-gather support) introduced a
DMA mapping API inconsistency resulting in dma_unmap_page getting
called on memory mapped via dma_map_single. This was seen when
CONFIG_DMA_API_DEBUG was enabled. Fix up this API usage inconsistency.

Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Acked-by: Anton Blanchard <anton@samba.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>