spi: use container_of_cont() for to_spi_device()

Some places in the spi core pass in a const pointer to a device and the
default container_of() casts that away, which is not a good idea.
Preserve the proper const attribute by using container_of_const() for
to_spi_device() instead, which is what it was designed for.

Note, this removes the NULL check for a device pointer in the call, but
no one was ever checking for that return value, and a device pointer
should never be NULL overall anyway, so this should be a safe change.

Cc: Mark Brown <broonie@kernel.org>
Fixes: d69d804 ("driver core: have match() callback in struct bus_type take a const *")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patch.msgid.link/2025052230-fidgeting-stooge-66f5@gregkh
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: gregkh

include/linux/spi/spi.h

@@ -249,10 +249,7 @@ struct spi_device {
 static_assert((SPI_MODE_KERNEL_MASK & SPI_MODE_USER_MASK) == 0,
 	      "SPI_MODE_USER_MASK & SPI_MODE_KERNEL_MASK must not overlap");
 
-static inline struct spi_device *to_spi_device(const struct device *dev)
-{
-	return dev ? container_of(dev, struct spi_device, dev) : NULL;
-}
+#define to_spi_device(__dev)	container_of_const(__dev, struct spi_device, dev)
 
 /* Most drivers won't need to care about device refcounting */
 static inline struct spi_device *spi_dev_get(struct spi_device *spi)