driver core: device: mark struct class in struct device as constant

The pointer to a struct class in a struct device should never be used to
change anything in that class.  So mark it as constant to enforce this
requirement.

This requires a few minor changes to some internal driver core functions
to enforce the const * being used here now.

Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Link: https://lore.kernel.org/r/20230313181843.1207845-11-gregkh@linuxfoundation.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>