spi: cadence-qspi: fix pointer reference in runtime PM hooks

Summary

In the Linux kernel, the following vulnerability has been resolved: Both cadence-quadspi ->runtime_suspend() and ->runtime_resume() implementations start with: struct cqspi_st *cqspi = dev_get_drvdata(dev); struct spi_controller *host = dev_get_drvdata(dev); This obviously cannot be correct, unless "struct cqspi_st" is the first member of " struct spi_controller", or the other way around, but it is not the case. "struct spi_controller" is allocated by devm_spi_alloc_host(), which allocates an extra amount of memory for private data, used to store "struct cqspi_st". The ->probe() function of the cadence-quadspi driver then sets the device drvdata to store the address of the "struct cqspi_st" structure. Therefore: struct cqspi_st *cqspi = dev_get_drvdata(dev); is correct, but: struct spi_controller *host = dev_get_drvdata(dev); is not, as it makes "host" point not to a "struct spi_controller" but to the same "struct cqspi_st" structure as above. This obviously leads to bad things (memory corruption, kernel crashes) directly during ->probe(), as ->probe() enables the device using PM runtime, leading the ->runtime_resume() hook being called, which in turns calls spi_controller_resume() with the wrong pointer. This has at least been reported [0] to cause a kernel crash, but the exact behavior will depend on the memory contents. [0] https://lore.kernel.org/all/20240226121803.5a7r5wkpbbowcxgx@dhruva/ This issue potentially affects all platforms that are currently using the cadence-quadspi driver.