soundwire: constify the struct device_type usage

Since commit aed65af1 ("drivers: make device_type const"), the driver
core can properly handle constant struct device_type. Move the
sdw_master_type and sdw_slave_type variables to be constant structures as
well, placing it into read-only memory which can not be modified at
runtime.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Ricardo B. Marliere" <ricardo@marliere.net>
Link: https://lore.kernel.org/r/20240219-device_cleanup-soundwire-v1-1-9edd51767611@marliere.net


Signed-off-by: Vinod Koul <vkoul@kernel.org>