spi/qspi: fix missing unlock on error in ti_qspi_start_transfer_one()

Add the missing unlock before return from function ti_qspi_start_transfer_one()
in the error handling case.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Mark Brown <broonie@linaro.org>

drivers/spi/spi-ti-qspi.c

@@ -376,6 +376,7 @@ static int ti_qspi_start_transfer_one(struct spi_master *master,
 		ret = qspi_transfer_msg(qspi, t);
 		if (ret) {
 			dev_dbg(qspi->dev, "transfer message failed\n");
+			mutex_unlock(&qspi->list_lock);
 			return -EINVAL;
 		}