virtio/vsock: check argument to avoid no effect call

Both of these functions have no effect when input argument is 0, so to
avoid useless spinlock access, check argument before it.
Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/vmw_vsock/virtio_transport_common.c

@@ -302,6 +302,9 @@ u32 virtio_transport_get_credit(struct virtio_vsock_sock *vvs, u32 credit)
 {
 	u32 ret;
 
+	if (!credit)
+		return 0;
+
 	spin_lock_bh(&vvs->tx_lock);
 	ret = vvs->peer_buf_alloc - (vvs->tx_cnt - vvs->peer_fwd_cnt);
 	if (ret > credit)
@@ -315,6 +318,9 @@ EXPORT_SYMBOL_GPL(virtio_transport_get_credit);
 
 void virtio_transport_put_credit(struct virtio_vsock_sock *vvs, u32 credit)
 {
+	if (!credit)
+		return;
+
 	spin_lock_bh(&vvs->tx_lock);
 	vvs->tx_cnt -= credit;
 	spin_unlock_bh(&vvs->tx_lock);