virtio_input: use virtqueue_add_inbuf_cache_clean for events

virtio_input: use virtqueue_add_inbuf_cache_clean for events

The evts array contains 64 small (8-byte) input events that share
cachelines with each other. When CONFIG_DMA_API_DEBUG is enabled,
this can trigger warnings about overlapping DMA mappings within
the same cacheline.

Previous patch isolated the array in its own cachelines,
so the warnings are now spurious.

Use virtqueue_add_inbuf_cache_clean() to indicate that the CPU does not
write into these cache lines, suppressing these warnings.

Message-ID: <4c885b4046323f68cf5cadc7fbfb00216b11dd20.1767601130.git.mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>