ARM: s3c64xx: make bus_type const

ARM: s3c64xx: make bus_type const

Since commit d492cc2573a0 ("driver core: device.h: make struct bus_type
a const *"), the driver core can properly handle constant struct
bus_type, move the s3c6410_subsys variable to be a constant structure as
well, placing it into read-only memory which can not be modified at
runtime.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ricardo B. Marliere <ricardo@marliere.net>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20240204-bus_cleanup-arm-v1-1-41d651dd8411@marliere.net
Link: https://lore.kernel.org/r/20240211-bus_cleanup-arm-v2-1-3de9e8af7cbd@marliere.net
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>