coresight: make coresight_bustype const

coresight: make coresight_bustype const

Now that the driver core can properly handle constant struct bus_type,
move the coresight_bustype variable to be a constant structure as well,
placing it into read-only memory which can not be modified at runtime.

Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: James Clark <james.clark@arm.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: coresight@lists.linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/2024010531-tinfoil-avert-4a57@gregkh