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

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.