rpmsg_virtio.c: fix get_tx_payload_buffer error

1. driver/rptun_notify_wait and driver/rpmsg_virtio_notify_wait may
return -EAGAIN, so if only judge status == RPMSG_EOPNOTSUPP,it will
cause busy loop in rpmsg_virtio_get_tx_payload_buffer;
2. remove redundant logic of continue.

Signed-off-by: Yongrong Wang <wangyongrong@xiaomi.com>

Author: wyr-7

lib/rpmsg/rpmsg_virtio.c

@@ -384,11 +384,9 @@ static void *rpmsg_virtio_get_tx_payload_buffer(struct rpmsg_device *rdev,
 		 * use metal_sleep_usec() method by default.
 		 */
 		status = rpmsg_virtio_notify_wait(rvdev, rvdev->rvq);
-		if (status == RPMSG_EOPNOTSUPP) {
+		if (status != RPMSG_SUCCESS) {
 			metal_sleep_usec(RPMSG_TICKS_PER_INTERVAL);
 			tick_count--;
-		} else if (status == RPMSG_SUCCESS) {
-			break;
 		}
 	}