virtio: fix test build after uio.h change

[ Upstream commit c5c08bed843c2b2c048c16d1296d7631d7c1620e ]

Fixes: d38499530e5 ("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>

tools/virtio/linux/kernel.h

@@ -23,6 +23,10 @@
 #define PAGE_MASK (~(PAGE_SIZE-1))
 #define PAGE_ALIGN(x) ((x + PAGE_SIZE - 1) & PAGE_MASK)
 
+/* generic data direction definitions */
+#define READ                    0
+#define WRITE                   1
+
 typedef unsigned long long phys_addr_t;
 typedef unsigned long long dma_addr_t;
 typedef size_t __kernel_size_t;