spi: tegra210-quad: Protect curr_xfer clearing in tegra_qspi_non_combined_seq_xfer

Protect the curr_xfer clearing in tegra_qspi_non_combined_seq_xfer()
with the spinlock to prevent a race with the interrupt handler that
reads this field to check if a transfer is in progress.

Fixes: b4e002d8a7ce ("spi: tegra210-quad: Fix timeout handling")
Signed-off-by: Breno Leitao <[e-mail]>
Tested-by: Jon Hunter <[e-mail]>
Acked-by: Jon Hunter <[e-mail]>
Acked-by: Thierry Reding <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-tegra210-quad.c

···
 	struct spi_transfer *transfer;
 	bool is_first_msg = true;
 	int ret = 0, val = 0;
+	unsigned long flags;
 
 	msg->status = 0;
 	msg->actual_length = 0;
···
 		msg->actual_length += xfer->len + dummy_bytes;
 
 complete_xfer:
+		spin_lock_irqsave(&tqspi->lock, flags);
 		tqspi->curr_xfer = NULL;
+		spin_unlock_irqrestore(&tqspi->lock, flags);
 
 		if (ret < 0) {
 			tegra_qspi_transfer_end(spi);