virtio: fix test build after uio.h change

[ Upstream commit c5c08bed843c2b2c048c16d1296d7631d7c1620e ]

Fixes: d3849953 ("fs: decouple READ and WRITE from the block layer ops")
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>