dma-debug: fix debug_dma_sync_sg_for_cpu and debug_dma_sync_sg_for_device
DMA-mapping.txt says that debug_dma_sync_sg family must be called with
the _same_ one you passed into the dma_map_sg call, it should _NOT_ be
the 'count' value _returned_ from the dma_map_sg call.
debug_dma_sync_sg_for_cpu and debug_dma_sync_sg_for_device can't
handle this properly; they need to use the sg_mapped_ents in struct
dma_debug_entry as debug_dma_unmap_sg() does.