mmc: core: constify the struct device_type usage

mmc: core: constify the struct device_type usage

Since commit aed65af1cc2f ("drivers: make device_type const"), the driver
core can properly handle constant struct device_type. Move the sdio_type,
sd_type and mmc_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-mmc-v1-1-1910e283cf5a@marliere.net
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>