rpmsg: virtio_rpmsg_bus: fix export of rpmsg_send_offchannel_raw()

Commit 8a228ecfe0 ("rpmsg: Indirection table for rpmsg_endpoint
operations") has made the rpmsg_send_offchannel_raw() a static
function and local to the virtio_rpmsg_bus module, but has not
dropped the corresponding EXPORT_SYMBOL. Fix this.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/rpmsg/virtio_rpmsg_bus.c

@@ -632,7 +632,6 @@ out:
 	mutex_unlock(&vrp->tx_lock);
 	return err;
 }
-EXPORT_SYMBOL(rpmsg_send_offchannel_raw);
 
 static int virtio_rpmsg_send(struct rpmsg_endpoint *ept, void *data, int len)
 {