Conform to the specification for GetStatus(), which states that "if there are no transmit buffers to recycle and TxBuf is not NULL, *TxBuf will be set to NULL". Cc: Leif Lindholm <leif.lindholm@linaro.org> Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Michael Brown <mcb30@ipxe.org> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>