virtio_caif: correct tags for config space fields

Tag config space fields as having virtio endian-ness.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

include/linux/virtio_caif.h

@@ -11,9 +11,9 @@
 
 #include <linux/types.h>
 struct virtio_caif_transf_config {
-	u16 headroom;
-	u16 tailroom;
-	u32 mtu;
+	__virtio16 headroom;
+	__virtio16 tailroom;
+	__virtio32 mtu;
 	u8 reserved[4];
 };