spi: tegra210-quad: Protect curr_xfer in tegra_qspi_combined_seq_xfer

In the Linux kernel, the following vulnerability has been resolved:

spi: tegra210-quad: Protect curr_xfer in tegra_qspi_combined_seq_xfer

The curr_xfer field is read by the IRQ handler without holding the lock to check if a transfer is in progress. When clearing curr_xfer in the combined sequence transfer loop, protect it with the spinlock to prevent a race with the interrupt handler.

Protect the curr_xfer clearing at the exit path of tegra_qspi_combined_seq_xfer() with the spinlock to prevent a race with the interrupt handler that reads this field.

Without this protection, the IRQ handler could read a partially updated curr_xfer value, leading to NULL pointer dereference or use-after-free.