include/uapi/linux/virtio_gpu.h: use __u8 from <linux/types.h>

Kernel headers exported to userspace are should these types.

Fixes userspace compilation error:

error: unknown type name ‘uint8_t’
Signed-off-by: Mikko Rapeli <mikko.rapeli@iki.fi>

include/uapi/linux/virtio_gpu.h

@@ -287,7 +287,7 @@ struct virtio_gpu_get_capset {
 /* VIRTIO_GPU_RESP_OK_CAPSET */
 struct virtio_gpu_resp_capset {
 	struct virtio_gpu_ctrl_hdr hdr;
-	uint8_t capset_data[];
+	__u8 capset_data[];
 };
 
 #define VIRTIO_GPU_EVENT_DISPLAY (1 << 0)